Hi elbeau...Welcome aboard..

Trading the 12'6" for the 11'2" sounds like a great idea.
As for the fins...1 fin..2 fins..3 fins..4 fins...I've even seen 5 fins...They all work ok.
I like single fins myself...I don't think it will pop out while turning on a steep wave..Is that what you mean?
I also don't see how it will effect nose riding...Some of the best nose riders ride single fins.
I'm no expert on nose riding or turning the 11'2" on steep waves...Greenroom or JB will know for sure.
btw...one of my friends has the 11'2" and he seems to have a larger fin than normal...I'll ask him if he changed it..and why...Here's a pic of his board.
DJ