Since I have tried to replay FO3 after several NV playthroughs, immediately deleting game after reaching Megaton unmodded, throwing it into oblivion for about a decade, I was looking for a mod like Oscuro's Oblivion Overhaul and a proper iron sight option to finally replay FO3 and touch it's DLCs for the first time (as my only one playthrough was in pre-DLC era).

If at first glance playing with mods like un-leveled lists seems to turn your game into a randomized chaos - it's not at all, as enemies and loot are defined by locations pretty well already (and there was already better leveling sistem in FO3 than in oblivion, by fact), except some wandering creatures which IMO should be not affected by player level as it can be easily avoided or killed with OP weapons like explosives anyway, while Simple Realism nerfs explosives & chems drops from enemies a bit. Looting stashes like the one in super-duper mart with this mods is more rewarding, yet you still can't find advanced weapons & equipment on raider bases (except ones that bethesda manually placed), even at level 30, as it is how vanilla FO3 was made.
And also while you leveling in skyrim, manually placed steel equpment starts to look out of place when chests and enemies around the same location have higher tier drops. There was no such effect in vanilla FO3 as there is no many different quality tiers of gear (which is good), and also even drops for maximum possible level is worse (yet still useful) than most manually placed weapons & armors you can find in the same locations. In that terms FO3 is already much better than skyrim or FO4, and turning level requirements to 1 in all leveled lists shouldn't break anything. It seems to be really balanced and immersive.

Simple Needs updated was chosen over other mods because it's lightweight, it can be easily tweaked in xEdit to be compatible with any other mod, and it works based on in-game time, with any timescale.

So, there is a compatibility patch for mods that I found most suitable for my preferences, with some minor changes and fixes.

Update:
- just replace old file with the new one. Don't forget to manually apply changes to global variables through console after loading an old save ("set ImperviousMult to 6" for example);

Installation:

1. Have an unmodified game, preferably GOTY GOG or steam (1.7.0.3, use anniversary patcher if needed), installed elsewhere out of program files directory
2. Run game at least once to generate settings&files in your documents folder
3. Install UUF3P ESM patcher
4. Install UUF3P, preferably manually (don't forget to copy "Unofficial Fallout 3 Patch.override" into your data folder), - OGG version; install FOSE 1.3.2b, Command extender, archieve invalidation. Run game to be sure it is installed properly (there is console command at UUF3P page to do so + if you start a new game without "Unofficial Fallout 3 Patch.override" or your mod manager ignored this file you'll see weirdly placed party hats at 10 y birthsday).
5. Install this patch + other requirements.

6. Copy "ISP_ConsistentSpread.ini" to "\Fallout 3\Data\fose\plugins\Tweaks\GameSettings"
It should contain this:

[GameSettings]
fAutoAimMaxDistance = 50000.000000
fAutoAimScreenPercentage = -180
fAutoAimMaxDegrees = 1.1
fNonAttackGunWobbleMult = 1.000000

7. Copy Stewie tweaks preset to "\Fallout 3\Data\fose\plugins\stewie_tweaks.ini", adjust it to your liking (note, that SR changes weapon animation speeds, so turning on fix for semi-automatic weapons will turn all pistols into miniguns, i've not decided yet if it would better or not to revert those speed changes and turn on stewie fix instead);

8. Check all files & set loadorder in any mod manager:
1) Fallout3.esm
2) Anchorage.esm
3) ThePitt.esm
4) BrokenSteel.esm
5) PointLookout.esm
6) Zeta.esm
7) Unofficial Fallout 3 Patch.esm
8) Goodies.esm
9) SimpleNeeds.esm
10) Impervious Power Armour.esm
11) FO3 NPCs Travel.esm
12) Faction Snipers.esp

13) <- if needed, localization files should be placed here, trimmed of any interactions with other mods in xEdit, so it should be compatible, but be warned to see a lot of english text

14) Simple Realism.esp
15) lo-fi_levellists.esp
16) lo-fi_levellists_dlc_patch.esp
17) lo-fi_solidworld.esp
18) DT in FO3 - No PA Scaling.esp
19) Iron Sights Plus.esp
20) True Weathers.esp (optional, not interfering with others, not touched by patch)
21) Explosive Entry.esp (optional, for this load order) (outdated, causes crashes)
22) Simple Needs Updated.esp
23) FO3IncCWPerLevel5.esp (optional, not interfering with others, not touched by patch)
24) Merged_eng.esp

All mods marked as "optional" can be removed or added later without starting a new game.

Install recommended mods if needed, fix load order.


To get full experience I highly advise to install this (you can install or remove any of listed below later, without starting a new game):

True Weathers - if you want more realistic lightning & weather without using ENB or ReShade;
Enhanced Camera - first person body & anims, no forced 3rd person view (it actually works fine with iron sight plus);

Essential graphic tweaks:
Sunlight fix
Viewmodel Shading Fix

Performance:
zlib Updated - to make loads faster on old PCs, or squeeze milliseconds on modern hardware (i do not see any reason to not update zlib anyway) + check "\Fallout 3\Data\fose\plugins\stewie_tweaks.ini" (performance options except heap size are disabled in provided preset)

Gameplay:
Anchorage Pulse Field Kills - to make anchorage pulse field dangerous
Increase Carry Weight on Level Up - if you don't like inventory management too much, as SR nerfed maximum load, especially for low str builds, I recommend to use 5 per level option. With -50% exp penalty and stong back requirement of 8 STR even with this mod you still have to rely on buffout during decent part of a game, so its just to reduce inventory management at high levels. DO NOT INSTALL THIS IF YOU WANT MORE SURVIVAL or  "true hardcore RPG" EXPERIENCE, as it's difficulty all about how much supplies, weapons and goods for sale you can carry.
 
Stability - got 1 crash in 8 hours, probably random, can't recreate it. Also game crashes if you press several buttons simultaneously in pip-boy repair menu
(which should be affected by nothing but stewie tweaks or UUF3P). Experience ZERO crashes (without NVAC) after turning-off all unnecessary options of steawie tweaks.
There is a tool for New Vegas for better exception handling to prevent some crashes - NVAC, which is working for FOSE too.
I recommend to play without NVAC at least some time (if you want to install it - don't forget to put it in fose instead of nvse folder).

This patch as mods required for it is not compatible with any other mod without proper manual check in xEdit (as not all of overrides that you don't want may be shown as "conflicts").

Changes (aside from listed in required & recommended mods):
- requirements for new perks from DT threshold mod rised to 7/8/9 STR & END;
- more creatures, NPCs, followers & loot now un-leveled (hope all of them, except CG NPCs (ones used in scripted scenes));
- level of NPCs, provided by lo-fi solidworld raised by 50% (to match levelcap 30 as it seems to be pre-DLC mod & because they gain only +3 hp/level due to SR mod anyway);
- NPCs & ghouls that got less than 40 base HP before now have 40, to match players base HP at least (there is still x3 limb damage multiplier that applied to general damage (x6 for headshots), almost any high level npc in basic game already have ~100 or 175 base hp WITHOUT endurance & level bonuse (& player got some DMG increasing perks), so rising minimum hp of low leveled ones to 40 only results that they not dying from any scratch, yet any raider can be one-shotted from stealth in range, even by complete non-stelth builds with SM 20 or die from 1-3 shots from a rifle or a good crit, & also because their levels is static now);
- base HP of simple realism high-level creatures with fixed stats now increased by 200-300 (yet still less than vanilla by ~300-500)
- HP regen from food almost removed (except some good food), bottled water heals only with "daddy's boy/girl" perk;
- no instant healing except from sanitazer bonuses or values of 1 hp;
- stimpaks restore only 1 hp/sec, but about 30% more overral;
- prices of power armor doubled from what it was in SR, to compensate un-leveled loot (which can lead to extreme gains even with 3-4 CHA builds) and extreme durability (and in SR it weights so much that it makes very hard to loot and sell anyway);
- hunger, dehydration & sleep deprivation debuffs to SPECIAL increased (otherwise SN mod gives no more than minor atmospheric changes due to the fact how much food & water in wasteland, + timescale of 1/24 instead of 1/30 means you can loot & gain more per 1 in-game day (personally i prefer 1/12 timescale, but due to paused time during dialogues & run speed i got like a month supply of food & water from springvale school and super-duper mart IN ONLY 1 IN-GAME DAY, so I reverted TS back to default SR value of 1/24) UPD - I sold all pre-war food and still have no problems, but I play with 5 carry weight per lvl mod (still have troubles carrying both some loot & big guns at lvl11);
- strong drinks now do not hydrate you, but heal with party animal perk, except for beer;
- some food values are lowered (as i think 5 iguanas on a stick is not enough for whole day); raw vegetables now give only 10% of daily quota;
- magaton bomb script of simple realism overriden by UUF3P (so 50 explosives requirement removed, I didn't figured out how to merge this safely and 100% bug-free as uuf3p uses diffirent & much heavier script(idk what it does), so i preferred to keep UU3FP changes as its last updated);
- perks which level requirements were raised by SR now got it back, perks which level requirements were lowered by SR - keeping this change - i made it to allow higher variety of choice a bit earlier to match un-leveled lists mod and -50% XP penalty from SR (also SR rises SPECIALs & skills required by almost every perk by 2 and 20, so you will be limeted mostly by you stats, not level, and you build specialization still affected by SPECIAL much more than in vanilla game);
- nuclear anomaly changed - now it has increased range from UU3FP & icreased damage from SR, hp required to proc lowered back from 60% to 20% to reduce chance of use without being killed or in relatively safe situations;
- educated now gives 3 points per level as usual (you still get 6 less skill points per level + you have -50% exp penalty from SR - so 28 extra points at lvl 30 will not make you jack of all trades anyway);
- frag mines now have the same range as frag grenades in SR; some explosions ranges increased a bit to match their damage tier (except for plasma);
- most short barrel guns (except laser) & automatic rifles, miniguns, rocket launchers now got part of their spread back. Double-barreled shotgun min spread lowered from 5 to 3 to at least match combat shotgun stats (as double-barreled shotgun have longer barrel). Plasma weapons have some minor spread. All spread values still 3x-10x lower than vanilla;
- SMG now have the same base damage as a pistols of the same caliber, but twice higher max spread (found that there are only 10 mm SMG, and no pistols or sawed-offs for 5.56);
- radiation poisoning effect changed to reduce endurance instead of health so you can sleep & wait now, minor STR & AGI penalties at high levels restored without deleting of new cyborg perk effect, which affects only endurance penalty;
- thoughness is now playable perk (in SR it was changed to require 2 more enurance, not hidden yet flagged as unplayable - which was not descripted on mod page, so many people cosidered unplayable flag as a mistake)
- scotch bottle model fixed;
- 99.9% of UUF3P & goodies changes saved (except mesh & texture replacements from iron sights plus mod).

There is potential problems that may be caused by ISP_ConsistentSpread.ini settings for SR, some restored gun spread values and iron sights plus mod as i did not test it (and currenty playing with this setup, having no scoped guns, almost not using VATS, all seems to be OK).

The problems are that real/shown VATS to hit chances may differ, VATS to hit chance may be calculated a bit wrong or bullets can behave weird outside of VATS, as i learned from discussions on this and some other mods - there is auto aim in this game that CAN'T be removed completely without completely breaking VATS (and aiming in 3rd person view), but can be tweaked to have zero effect outside of VATS while still keeping VATS working.