Hello,
have a look at this thread, especially on and other people replies :How to create planet size world? - World Creation - Epic Developer Community Forums
One thing is that you can do that but you’ll have to separate things a bit. creating your space travelling world with like the flying starter kit and search in this forum what people did to help you learn.
doing a fps or 3rd basic project with a level being your spaceship inside (and where you can go to seat in command center to go back to space for example)
and the how to do worlds that you’ll can check in the thread.
Edit : another interesting thread about planets : Simulate Planet Orbit? - Blueprint - Epic Developer Community Forums
This will be a lot of work but it will be a lot of fun too for you ^^ good luck 