new house electrical projects

The house I'm buying doesn't have any ceiling fixtures in any of the bed rooms just a wall switch that controls a wall outlet. There is attic access and Ide like to install ceiling fans in the bed rooms. I'm not sure what's the best way to attack this I want to run a 3 wire so I can control the lights by the switch and the fan by the pull chain on the fan. If I was just adding a light I could snake a wire from the switch controlled outlet to the new light but in my situation than the fan and light would both be controlled at the same time. My next option would be to snake a 3 wire from the fan to the existing switch and manipulate the splicing inside that box however I feel this may over pack the box considering there will be at least two cable clamps a device and at least 8 connectors. My third question is should I remove the box and replace it with a double gang to give me more room, the box how is metal and the cable is bx and if so how would I accomplish this ? walls are sheet rock not plaster.