You want to put the tub in first.
Tiles, or good quality paint.
No, it is better caulked with a water resistant caulk. ( Also it should be at least water resistant drywall or concrete/fibre board.)
Soak it in a tub of water for a few days, then the drywall can be scraped off.
If is is a fiberglass or steel/cast unit, they install while doing the plumbing rough, before insulation and drywall. The cultured marble/garden master tub installs after trim, before flooring.
Yes, as long as your drywall is in good shape, you can tile it.
Cutting drywall before you snap it .
You don't put 'spackle' on at all. After taping the drywall seams you 'mud' them with drywall compound. -It is a totally different substance from 'spackle', which should be used only to fill small holes and irregularities in wall.
You put post protectors in the drywall, and don't do it at the end of the drywall.
No, the prime coat can go on anytime.
The poly shield goes directly onto the frame before drywall.
Never heard of that before. The drywall may be very dusty, or the primer iwas not mixed totally.
Only if you put on a good primer first.