I usually consider the payload i\'m taking up first. Top down design. My cycle goes something like this. Make an orbiter with maneuver fuel, rcs, and SAS Test launch it. Does it work? Great, moving on. Build the lift stage. Is it stable? if no,Add ASAS to the bottom of the payload stage. if yes. Get ye into space. Did they come back alive? if no, remember to add parachute to the command module. if yes. SUCCESSFUL MISSION.