Yes, if there are staterooms available to choose from. If the category you want is in GTY status, then there are no rooms left to choose from, and you will get assigned a room by DCL.
On our Aug 2088 cruise we paid in points and were able to get a SPH room. I had checked online and knew that the SPH room was showing available, so that is the room I requested. When you call MS to book your cruise, they will help you pick your stateroom.
Absolutely! My family of 5, which included my mother, sailed on the Dream in July using only points. We booked 2 connecting 6B aft balconies and I requested the cabins I wanted when I booked.