The size of your project will depend on a number of things, such as packaging, which effectively nearly doubles its size (since it duplicates many of the files for the packaged build). Much of that can be deleted with no negative consequence, see here:
Ultimately however, the project file size may not matter as you may have a lot of unused assets simply available but not referenced in the game. Optimization will focus on what is actually being used; so, you’ll want to look further into it.
8K is high, perhaps 4K will suffice. Perhaps, converting as many textures as possible to virtual textures could help. Though, I’ve never attempted to optimize 8K, so I don’t know how effective it will be.
For shadows, you’ll want to look at shadow mapping and/or ray tracing. But yes, texture pool affects shadow performance.