Yeah, I think that would work if you want a drip catcher. Maybe put some sand in there so any stray poops don't glob onto the vinyl.
I haven't used the nipple-waterers yet myself, but heard good things about them. Chickens peck at new things, and pretty quickly learn peck=water. From what I've...
If you use water nipples on the pvc, shouldn't add much moisture to the coop. You could also add a board under, kinda like a poop board, to catch drips so they don't soak into your bedding (and so you notice any leaks).
I like the additional roosts. It's good to have more than one in case any...