For something that large you will want to use World Composition: World Composition in Unreal Engine | Unreal Engine 5.3 Documentation
You’re within the max size for a single level, but there can be issues at that size anyways since the precision will be lower as you get further away from the origin.
For something that large you can’t use baked lighting though, so you won’t need to unwrap an additional UV set for lighting. The issue is that you will have such a large area that it will use too much memory to bake the lighting since it has to load everything at once. Something that size would also take up a lot of disc space for the lightmaps.
The GPU is not involved in building lighting. Baked lighting is calculated using the CPU and the amount of geometry and textures is limited by how much RAM you have.