Here is stuff that is not necessary to know and is too long to put it into main description.

How to turn on console commands:
Open text file "The Witcher 3/bin/config/base/general.ini", add new line, paste text:
DBGConsoleOn=true
In game, use tilde ~ key to open console
Original game console commands: https://steamcommunity.com/sharedfiles/filedetails/?id=765050564

Сonsole command NL_GetPosition()
Pauses game and displays ok-dialog with current player position. It can be used with tptopos(x, y, z) command for precise teleporting.

Console command NL_AddStartingSet1()
Gives armors and swords which you start the game with. Nothing unusual. Except that original game does not provide any other legit way to obtain these items if you lose them.

Console command NL_AddStartingSet2()
Gives armors and swords which you start the game with in "Hearts of Stone only" mode. Compared to StartingSet1, this set looks exactly the same, but with better stats. Original game does not provide any other legit way to obtain StartingSet2. Chest piece is not upgradable to warrior's leather jacket, because its recipe needs item by ID "Starting Armor" from StartingSet1. While chest piece from StartingSet2 has ID "EP1 Standalone Starting Armor".

Console command NL_AddStartingSet3()
Gives armors and swords which you start the game with in "Blood ad Wine only" mode. Original game does not provide any other legit way to obtain StartingSet3. Chest piece is not upgradable to warrior's leather jacket.
In original game, this set has almost the same stats as StartingSet2. In No Levels mod, StartingSet3 items quality has been changed from yellow-magic to brown-relic, and has been given better stats than StartingSet2 to make things different and maybe interesting.

Console command NL_AddRavenSet()
Gives armors and swords from Raven set. Actually in the game it is called "Legendary Manticore". But it looks literally like Raven armor from The Witcher 1. Original New-Game (not New Game Plus) does not provide any legit way to obtain these items. In NG+ regular Manticore set items are replaced with Legendary Manticore items. Both these armor sets look differently, not the same as compared to other regular (NG) and legendary (NG+) witcher sets.

Console command NL_AddDebugSwords()
Gives 7 silver swords which have 100% chance for bleeding, burning, poison, freezing, stun, stagger, instant kill. Some swords also deal "fire", "frost" and "poison" damage, instead of regular "silver" damage. These swords are not part of original game and were added by No Levels mod for debug purposes. You can use them too at your own risk/fun. Swords, after being added, are modified using Potato Item Cheats, so if you remove No Levels and Potato Item Cheats, stats of these debug swords may reset or break.

Console command NL_TellTime()
Shows message with "ingame", "play" and "engine" times.

You can multiply all armor points of all player armors using modConfig.ws option playerArmorPtsMult and console command NL_SetPlayerArmorPtsMult(1.0). Note: 1.0 is default value, you can pass something like 0.5 and 2.0.

You can change armor points and damage type resistance multiplier for player during fistfight minigames. modConfig.playerArmorMultFistFight + console command NL_SetPlayerArmorMultFistFight(0.0 / 0.5 / 1.0). It is needed because if player has good armor, player becomes nearly invincible during fistfights. Especially during fistfights where Geralt does not have to take off his chest armor piece.

modDamage.ws option "m_randomMeleeDmg". And console command NL_RandomMeleeDmg(0/1). Allows to turn off/on random melee damage. Useful for research purposes, to see how damage works and see what deals how much damage.

There are versions of Nathaniel's "Iron Poker", Aerondight and Legendary Manticore (Raven) armor set with special stats. You can obtain and try them using console commands: NL_AddSpecialIronPoker(), NL_AddSpecialAerondight(), NL_AddSpecialRavenArmorSet().

Did you know you can use "laundry pole" (PIC_AddItem('Laundry pole')) and "fence board" (PIC_AddItem('Plank')), in your everyday fights, because their inventory 'NoShow' tags have been removed by NL?

Vesemir's swords have unique look, you can add them using PIC_AddItem('NPC Vesemir Steel Sword') and PIC_AddItem('NPC Vesemir Silver Sword') and then customize their stats using PIC_AddCraftedAbl (see "modNoLevels/extras/Potato Item Cheats/manual" and def_item_quality.xml for details).

Console commands which teleport you to other regions. Warning: some quests or points of interest may not work correctly if your enter new regions by the use of these console commands, before entering them through normal gameplay. NL_gotoWhiteOrchard(), NL_gotoWhiteOrchardWinter(), NL_gotoVizima(), NL_gotoVelen(), NL_gotoSkellige(), NL_gotoKaerMorhen(), NL_gotoIsleOfMists(), NL_gotoThroughTimeAndSpace(), NL_gotoToussaint().

NL_AddAllRecipes(). Adds all alchemy item recipes. Might be useful if you want to simulate NG+ in NG. Or max-out your "aquired tolerance" alchemy skill.

NL_Bolts(). Adds 1 bolt of each type to inventory, but only if you don't have it already. Only 1 is added because of weight limit. You can then select bolt you need more of, and use console command PIC_AddSelectedItem(50).

If you want to see item IDs or other details about these commands, you can find them in modNoLevels\content\scripts\game\modcode\modCommands.ws