1) You can find aluminum (or foil) tape at Home Depot, that's where I purchased mine. I wouldn't think it's too safe to use regular duct tape.
2) The binder clips would be fine, but just in case you should put something heavy on top of the top lid to hold it down.
3) That should be enough holes. Just make sure the humidity stays at a good level between 50%-60%, but if it gets lower than 50% even after a spray you would need to cover up a few holes.
4) Spraying the paper is just fine, just don't spray too much where you soak the paper and then your humidity will go well over 60%. All you really need to do it just spray the tub lightly (just a couple of sprays) with warm water and your good for a few days. I haven't sprayed since almost a week ago and the humidity is at a stable level.
Hope you enjoy those tubs.
Plus, I notice that you have a half log hide, just a side note that the log would not be secure enough for your Ball python, more stressful than secure. Get two, identical hides (for both tubs) that hug the snake on all sides and only has one entrance. The hides on reptilebasics.com work really well, I would suggest getting hides from that website.