Wheel whatever you can afford. The most fun I have ever had was in a stock Toyota or Jeep. Of course certain trails require a locker, the nasty ones need two...but you can go lots of places with what you have now. You can go ARB and hold off on the cromolly shafts until you save enough. Just carry a spare Birf and know how to repair in the field (camo method works well)
I think too many people get hung up on worrying about breakage, ratios, tire sizes blah blah blah when they could be out wheeling and having fun...which is the point of the exercise right?
(not saying thats you, just saying)