1. Any comments on my setup? I would make sure that you have two hides (one on each side). If you can't fit it, you can trade out the water bowl to something smaller for the time being. I also agree that the ambient temps are a bit low. What you can do (this will also help with humidity) is cover most of the screen top with a damp towel, foil, foil tape, glass, or plexiglas. This will help to hold in some of the heat from the hot spot. If your ambient temps are still low, then consider adding a lamp or CHE on a dimmer. I don't think you'll need too much. As for something to climb on, that's completely up to you. Ball pythons really aren't arboreal in nature, but some will climb on a branch if it's in there.

2. Are the temps alright? I covered this above, but your hot spot temps are fine.

3. How fast should I expect him to gain weight healthily? He wasn't gone for too long and ball pythons are well known for fasting. I would just keep an eye on his weight and make sure that he's always gaining weight. You might be tempted to feed him large meals, but I would stick to feeding hoppers for two or three weeks then he can bump up to adult mice for a week or two and then up a size again. If you have access to rats, now would be a good time to get him started on those. It will be more convienent for you in the future.

4. Any tips for how to get the gunk off him (he went over one of those sticky mouse traps..) Make sure that he didn't injure himself. Those can pull off scales if you aren't careful. You can try soaking him in warm water (85-88*) with a drop or two of dish soap. See if you can work it off with a wash cloth. If you can't (don't rub too vigorously), then don't worry about it. He'll probably go through a shed cycle pretty soon and it'll come off with his skin.

5. I plan on feeding once a week. Should I start that now or does he need another mouse tomorrow because of his fast? Like I addressed above, just feed him weekly and start off with small meals and work your way up. He'll regain his weight back in no time.

6. Any other comments at all? I think you've got most of your bases covered. I'm glad you found him!