I think generally unless you go crazy with poly limit like 100-300k and above you can get away with a lot of geometry. What it really comes down to is modularity and smart use of textures. IE can you take a Building and then kit bash that thing into 3 more buildings using some UV tweaking, vertex shading and shader based…
You mean 2048x2048. Actually 3rd person games require less detail than first person, 1024x1024 would be near the high end for current consoles, you should be able to get away with 1024x512 or smaller for non-key buildings, but if you are sharing texture sheets well you can get away with bigger textures. 4-10k tris should…