Aang replaces Luffy and fights all the battles Luffy has been in to see how far he can get.
The Story stays the same no matter what. He gets his crew members all at the same time he got them in the story. and stuff like that. If Luffy did not win the fight Aang doesn't have to.
Speed is Equal to Luffy's at that time.
Luffy is in a regular state but gets all his AS feats.
His Morals are on.
I'd say he stops at Alabasta. Not enough Moisture in the air for him to use water against Crocodile.