Hi, I'm finishing my basement and have a light that is already on a separate circuit. The circuit also has at least three additional lights on the circuit. The circuit is wired with 12 gauge wire and it's on a 15 amp breaker. If I want to control that one light with a switch and also add on two outlets, don't I have to upgrade the circuit breaker to a 20 amp breaker and control the light with three wire? I'm actually surprised to find that the 12 gauge wire is running to a 15 amp circuit. Thanks

If ALL the wiring on the circuit is #12 there is no reason to limit yourself to a 15A breaker.

The rest of it you lost me. Can you try to explain a little bit better?

It all depends on where the wire is now, where you want the switch and outlets.
I drawn you three lights (presumably on pull chains), a switch and three outlets. Is this what you want to do?