A three part modular base sounds good and doable to me, spent plenty time doing nonfunctional custom builds like this
Figure launching collections of parts that can be assembled like so:
A) launchpad; does nothing by itself but offering a landing target
B) fuel refinery/station; refuels rockets on the pad
C) parts factory; allows construction as on Earth pad, have a drop list of completed pads to load from build screen
Make this a total pain to build with hundreds of heavy parts, but easier after the first based off the moon or wherever;
Parts don’t all have to be unique, maybe wonky looking as it’s built but then *poof* it turns into a nice background pic when the last piece is added