I want to see a really good post-game or NG+. I liked Three Houses' because it cut back on the tedium like building professor level and gave options for building units in ways that would never work in a NG file, but it didn't really change the experience of the game, so I want to see something that changes a lot (although it wouldn't work that well with multiple routes).
Have you tried FE4 or FE5? They don't have exactly what you describe, but inventory management is very important in both games, and in both there are 7 item slots for each unit's inventory.
In FE4, managing inventories is a lot harder because you can only trade by selling and buying stuff to and from the pawn shop in castles, which can be quite difficult because every unit has their own gold pool, and you only sell things for half their value. This sounds like a pain and most people will say it is, but I personally didn't mind it because weapons and items are very potent and freely trading something like a 50 kill Brave Sword or the Paragon Ring would be ridiculously broken. The one thing I don't like is that you have kill boss who drop items with the unit who wants the item if you don't want to go through the Pawn Shop process.
FE5 is much less restrictive, and the weapons and items are a lot more limited because stat boosters are permanent and weapons and staves can't be repaired without using the Hammerne/Repair staff. However, you can trade an infinite amount of times on Player Phase which is very useful considering the scarcity of weapons compared to most FEs, and trading Crusader Scrolls to units close to levelling is fun. Capturing is the main way of getting weapons and you need to trade with enemies that you've captured to take their stuff. Thieves can also take whatever they want from enemies as long as their faster and have higher Constitution than the item they want to steal (Con can also increase on level up unlike GBAFE). Also unlike FE4, being able to trade normally lets you trade another unit's inventory so they equip a better weapon for Enemy Phase (for example, using an Armourslayer on PP but equipping a magic sword for EP).
I definitely think both of these games had more in-depth inventory management than FE7, and Mines and Light Runes didn't really exist - there were only 4 Light Runes on Eliwood Mode, 3 on Hector Mode, and 5 Mines (and 1 of the Light Runes is mutually exclusive with 1 of the Mines).
I think she does in her supports with Dorothea, in particular the A and B.