Outlets per circuit
Electrical codes require an outlet every twelve feet, not as a guide to how many outlets you should have in a room, but so as to minimize the amount of exposed cord that runs in a room. Locating an outlet every twelve feet means that an appliance will not be more than 6 feet from an outlet at any spot along a wall.
As such, the number of outlets per circuit depend on the particular circumstance, not some general rule. A Kitchen can get six circuits that run to just one outlet (one for the dishwasher, one for the microwave, one for the garbage disposal, one for the range, and two for the outlets around the kitchen), whereas the rest of the house can survive on two or three other circuits. If you have large stereo equipment or lots of computer equipment, you might want to add a circuit or two for each one.
Thus, the rule is to roughly anticipate how much energy that you will use on each circuit, and plan accordingly. To just meet Code for outlets that you do not plan to use, you can use just one circuit for all of them.