Sitting in gear isn't bad for the clutch, but it ages the throwout bearing. Same thing for coasting with the clutch pressed. Throwout bearings last a long time, are cheap, and are replaced any time you pull the tranny for anything. I wouldn't be worried; what you're doing is pretty much what it's made for. Just don't ride the clutch.
In some states, at least AL, it's illegal to coast in neutral, which is a stupid and unenforceable law. Might have had a reason for it back in the day, but it's inked on a page somewhere and needs to be scratched out. Coasting is good, especially these days. Random info!
Powershifting is definitely bad for our clutches, but most people don't know what that really is. Shifting fast at high rpm is ok if done smoothly. Powershifting means leaving the throttle on the floor and shifting as quickly as possible without lifting. On some cars it's worth a few tenths in the quarter mile. If anyone actually does regular burnouts, then they should know the risks, and have bigger things to be worried about.