2 boxes should be fine.
I personally don't switch to layer until they actually start laying, but many people feed it when they're "close enough" (18 weeks+) so up to you and what's convenient for you.
As far as nest placement, I'd say make it more convenient for yourself. Just keep them lower than roosts. Chickens aren't too picky about where the boxes are. Though my personal preference is also to have them at least a couple feet from the pop door, so any muddy feet get "wiped off" as they walk across the bedding.
I personally don't switch to layer until they actually start laying, but many people feed it when they're "close enough" (18 weeks+) so up to you and what's convenient for you.
As far as nest placement, I'd say make it more convenient for yourself. Just keep them lower than roosts. Chickens aren't too picky about where the boxes are. Though my personal preference is also to have them at least a couple feet from the pop door, so any muddy feet get "wiped off" as they walk across the bedding.