Since you are in your 20s, there is absolutely no reason why this will be your last RTW trip. Why try to do ėverything now? Just go to a few places and do them properly. Go back to the other's later on. And remember, always have a few trips planned, booked or even thought about before you start the first one. That gives you something to do when you get back - rather than feeling sorry for yourself because "we're back".