Any advice on clickbank upsells and how it works on clickbank?

Once my first product is approved, I want to stat working on an upsell, but I have no clue how upsells work on clickbank. Is it once they buy, they are brought to my upsell page instead of my thank you page? And if that it how it is, then when they buy the upsell, which thankyou page would they go to first, or do I make a new thank you page where it has download links for the upsell too? Also should I write out like a long sales page for the upsell, or have it super short or what? Also I'm planning on having 2 upsells, is that good or should I have a lot? I don't want to overwhelm customers, pretty much I want them to pick a cheaper or more expensive upsell, one or the other... would it be the more expensive one pops up first, and if they buy they don't even show the cheaper one, and if they refuse the first offer, then they show the cheaper one, or even if they buy my upsell will it still try to get them to buy another one? Dang, it'd actually be pretty fricken awesome if it stops offering once they buy because then yea, I could make like 4 upsells, offer 97 reject offer 27 reject offer 67 they accept and it doesn't even show offer 17. Something like that, or if they bought the 97 offer at the start, then clickbank won't even offer any other of the upsells, is that how it works? That would be awesome! I don't know anything about it and can't findmuch info on youtube... I'm really curious on how upsells work specifically on clickbank so I can start strategizing...