There are several types of paint you can use depending on the result you would like to achieve and the area you are covering. Matt, eggshell, satin and gloss all can be used on drywall with different finishes.
You use drywall primer first. After that you can use any normal paints.
After your basic drywall primer you can use any paint you wish.
It's generally much better to use water base primer on drywall.
After drywall primer it can.
You use standard 1/2 inch drywall .
what kind of paint does O'Keeffe use
noo!
If you expect your shower to last, then remove that drywall and re-finish it with concrete/fibre board. It's so much better than drywall you wouldn't believe it. Nobody professional does drywall around a shower anymore.
Yes, you can.
Use a sealer if the drywall was damaged while removing the wallpaper, then use a high quality latex paint in the sheen of your choice.
Yes you can. Best sand it lightly for for any bumps - I use a regular drywall sander on a 5ft. pole for this.
Drywall primer should be used.
The usual kind of oil paint.
If by top layer you mean the paper, then re-install drywall on that wall.