I have begun working on end game study and this is my first real effort.  As all the literature on end game suggests I got the King involved right away and that seems to have helped a great deal. 

Please let me know if my ending choices were sound.

22..Nb8 is actually the move that wins a piece for black, although you have an ugly white pawn storm on the queen side to potentially deal with.  Note that white simply has no way to deal with the double threat on his bishop after Nb8.  I should mention that even down a piece, I'd still be tempted to play white - I think all those passed pawns are bound to score.  But I just wanted to point out  where you actually went up a piece.

Incidentally, I disagree with your analysis that white's bishop is "useless" - it can take control of any light diagonal on the board because of where white's pawns are placed.  You were wise to get rid of it.

A small quibble on 27..Nxa8.  Why not take with the rook and get it out from behind those doubled pawns?  I would be quite comfortable playing white here...black needs to take out those queenside pawns, quickly!

I'm trying not to analyze everything here, but white gives himself a backward pawn with 28. b4?! and then further weakens it with 29. Re7.  While getting your king into the center should definitely be a priority, I would be tempted to play 29..Rc8 and really force white to sweat about his poor pawn move.

Although I would have played your position differently, 31..Kd5 was an excellent move, given the position.  But notice that 32..Kc4! would win either white's c or b pawn.  And white would not have been able to play 33. b6 which made your position much trickier.

35..Ke4?  Definitely a mistake.  You need to take that b7 pawn more seriously.  You were right not to play Kc6?? which loses the knight to 36. d5+, but you need to put the king on d6 and circle over to that pawn.  You lucked out that your opponent didn't move his b, c, and d pawns together, where I really think he might have won the game.

So to wrap up my comments, I think you had some good instincts about putting your king in the center, and your trap on the bishop with 22..Nb8 worked well.  But giving your opponent a big pawn storm like that is not recommended!  Fortunately, your opponent helped by not pushing his pawns up the board together, where you would have had a much harder time hanging on.

Hope my comments helped, and good luck in the future!

Doesn't 25...Bd6 win a piece?

Of course white gave it to you anyway with 26.Nxc7? (instead of 26.Re2).

Those pawns are worth at least the knight, and are worth more each time they get to advance.  Letting your king blockade 2 of them was a blunder, and after that you're winning. 

This was much more dangerous for black than you gave it credit for.