I myself an ambidextrious in everything I do...(I.E. I don't have a prefered hand) And I choose to fight south paw. Of course my first trainer was a south paw so I was slightly bias. But you bring up a good point...Some of the basic offence you learn in boxing is difficult for a south paw fighting against an orthodox fighter...but you have to look at the reverse as well. When a righty is fighting against a south paw, because of your stance and the way you hold your guard he will have the same difficulty as you do. I don't really belive in training a set group of combinations I think it is important for a fighter to find his own style and his own way to feel comfortable.. But I will tell you from experiance, the hinderance and advantage are even on both sides.