"1.It must be easy to intermediate difficulty (no returning from the surface of Eve, etc.)" Whattt. That's easy! Just think small and dont over engineer.
This is what mine has A place to store kerbals Lots of solar Panels (A girder or two with a few Gigantor XL's) A place to dock space planes and ships A fuel tank hangar with fuel tanks A winch to bring things closer to dock.
Geosynchronous orbit over KSC isn't the easiest thing. Correct me if I'm wrong but the only way to get there without waiting is to go straight up and not do a gravity turn.