Re: Wall to ceiling joint
Unless there is a reason otherwise, I always leave a 2" to 6" strip of the wall intact so that the wall/ceiling joint is never disturbed. Tape your new drywall into the strip that's left behind, being careful not to goop up the ceiling. When you're done, you've got a new wall and the wall/ceiling joint was never touched.
If it's too late for that, install the wall board. Rather than taping the joint, use a fire rated caulk, then install crown molding to hide the joint. you could tape it if you're super careful not to tape out beyond what the crown will cover.
I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!