Rulebooks about handling multiple NPC characters and managing Party resources?

At some point I want to go back to running D&D for my friends but I'm changing some things around. In order to make things more fun and satisfying for some of their characters, in addition to letting them reclass, I was going to add mechanics for food/drink consumption so they'd either have to forage for food (it's middle of winter in the campaign time) or buy in bulk from a town (the country is in the middle of a civil war and is running low as is).

In addition, the party has a habit of picking up and adopting NPCs in most of my campaigns. There are more fleshed out NPCs than there are party members and they have expressed no issue with stopping. At some point it's going to reach Fire Emblem levels of the number of colorful characters. On top of the foraging rules, I was wondering if there was anything that gave pointers to how to have the NPCs interact with the party on top of their own wants/goals/plotlines.

While I search on my own, is there any well-known source books that fit my needs? It'd be really nice to know if someone had a similar need for their game.