Need some help with wiring (House)

If it is a 20 amp breaker, then all the wires on that circuit must be 12 gauge. Think if you used 14 gauge on the 20 amp breaker for lights and the light socket shorts out. Then the 20 amp breaker may not pop to save the wire from melting and starting a fire.

Aren't you putting in at least one outlet in that room? I suggest you add one and make it a GFCI.