A friend and I painted my CB450, and the prep work - primer, filler, and sanding, was the biggest part of the job. I used two-part paints, because that's what was available to reproduce the factory colors. They take careful measurement and mixing, and have limited life once mixed. I also added some color to the first few coats of clear, to give that 'candy' look, and shift the color closer to OEM.
I would recommend a two-part hardening clear coat for the tank, since it will resist exposure to gasoline better. You have to give it time to harden some before the final fine wet sand and buff, but not too much time, or it gets too hard. Also, take extra care with masking around the filler neck, so gas doesn't get under the paint.