I am in the process of buying a house (3 years old). The walls are already
painted.

Rooms as follows.

Living room 20' x 16'
Family room 20' x 16'
Bed 1 15' x 11'
Bed 2 11' x 10'
Bed 3 11' x 10'

They all have 9' ceilings.

Approximately how long will it take to paint the walls in these 5 rooms?
Should I try and get a larger 12" roller (or even larger) - although I
believe the largrr they are, the more difficult they are to use due to the
additional weight of the roller and the paint.
I guess the walls will require 2 coats of paint.

Thanks