how much can i have on a 20 amp breaker?
Add up the wattage on the lights, the stereo gear, the fan, and the TV, then divide by 120 and see if it's more than 20 -- although unless you have a monster amp on your stereo, I doubt you'll run into trouble there.

As to the receptacle itself, it's fine -- Code only apportions 180VA per receptacle yoke or lighting outlet.