My son is just slightly younger than yours so we're dealing with some of these things too but thankfully he didn't like pull-ups so we didn't have to go through that extra transition! At the time I wanted him to wear them, but I'm glad it worked out that way!
A couple of thoughts: if there are any kids he knows who wear underwear, casually mention it to him. My guy was ready to train physically, but he didn't want to until he found out his little buddy was wearing big kid undies. We also made a big deal out of picking out underwear - he really wanted the Cars ones, his favorite movie at the time.
Propaganda. I find that if a book or a video can say it instead of me, the message goes a lot farther! You could see what your library has about underwear.
Like I said, we never did pull-ups, but I know it helps my son to have some time to get used to a change. We'll tell him, "in so many weeks, you're going to ..." Obviously he doesn't really understand how long that is, but he seems to understand that this change is going to happen soon but not right this second. He might be upset at first, but by the time we get to the actual change, whatever it is, he's usually just fine with it. I think if you show your son his supply of pull-ups, and tell him that once they are gone, he's going to wear underwear. You could keep the bag out so he can see how much closer he's getting to that day, and remind him casually once a day that when he's done with them he'll get to wear his new big kid undies.
As for the wiping, I only wish mine wanted to wipe himself! I think that's awesome. You could try what I do when we brush teeth - my son gets a turn and I get a turn. That way he gets to feel like he's doing it on his own, but I know that his teeth are actually getting clean.
It sounds to me like you're doing a great job! Good luck!