I have a 34" waist but my legs are only...
I have a 34" waist but my legs are only 21", are the legs loops going to be to loose if I get a size large?
I will be using this on both a Ropes Course and on an artificial climbing/rappelling tower - is this going to be a good choice?
I need to be able to clip in on both verses having to tie in while on the tower.
You should be good. You can always exchange it if not. It sounds like you need either a medium or large, but I would go for a large. This harness is one of the best out there, it'll work great for the tasks you described.
if your leg loops are a little loose, you can adjust the strap the controls how far down they hang. as long as the waist is tight enough, you are safe.
if you're working in those settings, you'd probably be happier with more support and padding.