Both of you have great comments. I just went through them all and Fritz agrees with all your suggestions (well, except taking that Knight instead of the Bishop, strangely).More importantly, they make good sense.

 Tempo: I needed to be reminded that the endgame is about one goal: promotion. I just added it to my 'things to remember before I play' list.

"11. ... Qd7 giving me a piece." What was the alternative? 11. ... Nc6? 12. Bxc6 bxc6? 13. Qxc6 picking up the rook. 11. ... c6 12. Bxd6.

"Trade pieces" is a common (and useful!) piece of advice because it's something you can do. But you should really know the ideas that make this the right thing to do. My guess is that you know them, but they are easily forgettable during the game. My understanding is that trading pieces is a means to accomplish the goal of eliminating counterplay. In your game, the f8 bishop doesn't really contribute to your opponents counterplay, especially not compared to the e5 knight as Tempo pointed out.

Fritz might like 20. Nf5 heading for Ne4 where you can jump into c6 and d6.

On move 28, it's hard for me to argue with winning a pawn, but 28. h3 (or f3) and you force a trade of your opponent's last piece. You can then chase down all the pawns you want.

How about 39. BxN. What happened to trading the pieces!? I think you'd win easily with your extra knight. If that doesn't look like an easy position to win, then you're right that you have some endgame study in your future.

20. .. Nxe5 Of course it is good to trade all pieces! Pawnstructure considerations are quite useless when a piece ahead. But it's better to chop his active knight off in stead of his bad bishop.

 The amount of invested tempo's doesn't play a role. You can only lose tempo's during the opening. Once developed, there is only the position. The difference between to fall asleep over your work or after your work, so to speak.

Move 22 Rad1 does nothing. Why bind a rook to defense?

Move 24 Kh1 no reason for such extremely passive move. If you insist to move your king, walk to the center.  A more sensible plan is to play your knight to e6 or c6 and to double the rooks on an open file.

Advise for the rest of the game: stop giving your pawns away for no reason:)

You must acknowledge your goal: queen a pawn. So:

1. defend your pawn 

2. clear the blocking piece in front of your pawn

3. clear the path to promotion. Use your king, so penetrate the enemy position.

4. push your pawn under good protection. 

In the negative: prevent your opponent from doing likewise.

Further:

1. Invoke weak pawns

2. Fix them

3. attack them