I don’t really have answers to your questions, but I can comment on the way I work for MSFS, compared to previous sims. I’ve developed for all the MS sims and offspring since FS2002, and modelling goals have certainly changed:) At the moment I’m working on a MSFS version of an airfield which I first built for FS2002 a long, long time ago, and since completely rebuilt from scratch for FSX/Prepar3d. I started with 512x textures, each with around four hangars, moved to 1024x textures per hangar for FSX, and now I’ve gone to 2048.
The 2048 textures are a bit of a compromise, but I like to build textures the old-fashioned way, with my own photos, and now I use a combination of Materialize and hand-editing for PBR.
Anyway, the point I want to make is that if your buildings are roughly similar to the one shown, then I wouldn’t worry too much about adding geometry, it isn’t as if each one is hundreds of thousands of vertices. With MSFS I have started to model a lot more detail for what is probably a similar airfield to yours. In the past I’ve relied on the photo texture for doors/windows etc for buildings further away from the taxi area, and used basic geometry for those up close to the viewer. Now I’ll model everything, including lights etc.
I’m not sure if my project would be affected if I went to 4096, but I’m not going to take that risk. And since I don’t paint my models using a PBR tool, I can’t just re-export at 4096 to test it out.
I don’t use Blender, so I’m no help with mapping, sorry.