The formula for area of a wall is length times height. So you would have
8' x 10' x 2 = 160 sq. ft. 8' x 11' x 2 = 176 sq. ft. = 336 sq. ft.
From that you can subtract windows and doors using the same formula.
Most paint covers (realistically) about 300 square feet per gallon. And you'll want to use two coats, so you would need two gallons.
Primer is only necessary for bare surfaces (like new drywall) or if you're doing a drastic color change.
You do want to make sure you clean the walls and patch any nail holes, dings, etc. Some painters will run a drywall screen over the entire surface of the wall just to knock off any high spots for a smoother finish.