60000 might be over. I you move the blocks closer to the origin and rebuild the light and it looks ok, then that’s it.
Like I say you can fiddle around with origin re-basing, I helped someone with that recently, but they had no other option.
With level streaming you just have lots of separate levels and they are added to one central level ( the persistent ). You can stream any level when you want. They can all have separate lighting / everything. I think it’s the way to go, and I know about it 
You’ll need to do the streaming with blueprint ( a lot of tutorials assume you’ll be using streaming volumes, but that’s more of an open world thing ).
Tell me if you’re interested and I’ll show you how to set it up…