changing old 120v wiring in 54 year old trailer

Hey thanks...good thoughts, but you might be over my head some. I do want to put in a window AC at what would be the end of the circuit, hence the 10 gauge and 30 amps. Siding is off, ha ha, just a 1 by 4 skeleton at this point. There are currently some dual 12v/120v lighting fixtures I am going to try to re-use. So I would need a 30 amp breaker for the AC at the box, and that should be the single breaker for the otherwise not-too-complex circuit that runs through the trailer?