Hotspot texturing is really easy to set up and super fun! I highly recommend trying it out.
As far as the base file size, I guess there's probably not much that can be done about that. Also, I Just looked at one of my bigger project files for reference, which is a little over 2gb. The folders for Blueprints, animations, meshes, levels, etc. are all under 100mb each. The sounds folder is around 250mb, and the textures folder is 500mb+, even using my methods. So, it seems like sounds and textures are where the bulk of the data comes from (at least for the types of games I make), and even my textures folder is twice as much as the sounds folder. If I were using mostly 4k textures, and per-object textures, the folder would be multiple gb. So all that to say, I think the textures are where you really need to pay the most attention if you want to keep the overall project file size low. I've worked on projects with other companies who used asset packs, and they were well over 100gb, mainly because of the textures. But yeah, as far as the base size, that's just the cost of using Unreal haha. I'm also not sure about how the data changes once you package the game, as the build will add new files, but in my case, the built file is either roughly the same size, or smaller with larger projects. Anyway, there's some more anecdotal information for your consideration! Cheers from America!