i only hopped on a tramp with my board a couple times but it was always fun. id recommend using a old beater board so you dont have to worry about taking the tape off again cause you're gonna wish you had that tape on there if you slice through your trampoline and fall through while jumping.
also while it is fun and helps you a lot its not substitute for actual practice on the hill, more of a way to just train your muscles and get an idea of how it should feel. when you have actual downward momentum its gonna feel a little different then it did on the tramp.
as for the straps thing i usually just strap down to right when its snug, i never tighten it more than that but i also dont ride it super loose, if anything ill have it a notch or two before being snug if i plan on just riding rails. just keep practicing and you'll be able to twist and flex your body the more comfortable you get with it. maybe try practicing some stretches or yoga if you feel up to it. im a big fan of yoga but i dont do it nearly as much as i should.
hope that helps a little.