Tier 4 armor and clothing settlements vendor sell unique outfits or armors, like companions outfits or minutemen general armor. Added shipments to vendors: armor trader sell lucas shipments, weapons sell cricket shipments, bar sell glass, crystal and oil, clothing sell anti-balistic fiber, leather and cloth , misc diamond city surplus, tier 3-4 a unique selection, clinic acid and antiseptic on tier 3 .                                                                                                                                                                                                                                                                                                                                                                                                                                                                            More food and drinks, even silt bean and tarberry added to restaurant workshop trader, rare drugs (calmex, daddy-o, x-cell and day tripper) and general drugs added to clinic depending on tier (i can't find the tier 4...) so you don't need to have high intelligence to create them, added more "rare" and general clothing, tier 3-4 armorers sell nuka raiders armors (tier 4 an unique "suit" from far harbor), weapons trader sells larger quantity of ammo  (may lag a little bit when trading whith them depending of quantity, mod added weapons...).  Now, there is several armor/weapons mods added to tier 3-4 armorer or gun shops, including ballistic weave's for tier 4 clothing seller. You can buy instead of craft with a requirement of 3 perks point, 6 charisma and level 14 minimum. You can add other mods items as well in their own leveled lists added by this mod, if they are not already added via a script (may require a tier 4 merchant).                                                                                                                                                                                                                                                                                                                                                                                                                            
Other thing: constructing the last tier shops cost less (3000 to 2000 for weapons - armor for example) and require only rank 1 of caps collector for all of them, including clinics. It edits leveled lists of  workshop vendors "container" and i create unique leveled list for the two last tier, i don't have the ability to add it via script for now. Everithing should be in english, i think i haven't edit names, it should be ok for all language. I mod little things for myself normally, in french, but because i can't find something similar, i share it.

A non-standard version is in progress for now, adding local leader unique cooking recipes (some of them are in "images"), 6 are in test, and have some references from New Vegas. More ammunitions and reworked conditions with no cap collector requirements, but i highly suggest a mod to rebalance the economy system with it or it may be too easy. Less weaves also. If you have a problem to install an armor or weapon mod (or if it is does not correspond entirely to the original mod when you try to install it, generally placed in the bottom of the list), try to drop it before, it works for me.

 So there is some writings error (french is my first language), nothing too bad. Si traduction a faire il y a, vous pouvez le faire ici ou la confrérie des traducteurs peut me le demander, je modifierais la permission si nécessaire.                 

For details of what is added, please read the sticky post.
Standard version added: require now the 3 main dlc's



Small tips and spoiler: tier 4 junk specialist is in goodneighbor hôtel, tier 4 clothing specialist, Anne,  is in WRVR broadcast station, the others are in vanilla random encounter for now.
Tier 3-4 settlements merchants have a very large selection of items with this mod, almost all you need without another crafting perks.

Remember that the linked settlements via supply lines shares their stocks. So, if you buy all items from a tier 3 clinic(for example), the other ones will share their inventory, so they will propose nothing. Caps and what you sell to them will be in their stocks too. They restock every 2 or 3 days i believe. So, do not establish supply lines for every settelements if you want to have more to buy/sell.

If you are low on caps, try to sell tools to Calvin at vault 81. Each one gives you 15 caps. Railroad secondary quests give also good rewards. BOS quests involving farms are a easy way to collect caps if you can pass the hard speech check.
An other easy way to make caps is to complete vault 88 quest from vault tech workshop and install a lot of slot machine with the option "indentured servitude". Each one generate 3 caps per settlers each day. Check "slot machine" on the fallout 4 wikia for details.

A known way to have an illimited settlements construction capacity is to drop weapon mods, not the packaged one but but the others with more details, visible weapon parts. No need to have any perk or mod just construct 5 of each (at a minimum of 6, you have to select a number to drop and lost some time) and drop them all. Then open workshop menu and store them. You can take the mods again after and repeat the process as many time as you wish. The construction limit depend to the details of the object constructed/stocked/scraped apparently. The population decrease your limit also and you cannot have more settlers near to the end of it, i have observing that recently. It makes sense but if you don't know it, you may miss it.

Some tier 4 merchants aren't even enabled... here is their id: Ron(barman): 00192357   Scribe(armor): 0010d56d    Doc A.: 00190047   Larry(weapon): 0002f2a7
To enable them, try: Prid -enter the selected ID-  enter, then:   enable . To move them to you, after that:  moveto player
I was having no other choices to make them spawn in front of me. They never showed up, or very rarely after hours or days of playing.
Ron Staples is bugged and will have tier 3 inventory, or disapear. I have not find any working fix for now. Tier 4 merchants still need a patch, they are bugged. 

Recommanded mods: Rebalancer - Gameplay balance center - If you have too much caps in your pocket, try the module "barter", i suggest medium version or even hard for very though traders. You will need more charisma, perks or chem to have the best price possible. In medium for example, with two ranks of cap collector and 12 charisma, you have not the best price possible.

Greedy doctor: "Doctor are rare todays" but it cost a very low ammount of caps in fact. This mod change that.

Classic fallout ambient music: Add the good old fallout 1-2 music to the game.

Npc level scaling: If you find ennemies too weak, you could try this. Read the description as always.