One thing about wetsanding- when I tried it with a hard rubber block, I found it loaded up too much. I tried it by hand which worked ok. What I finally ended up using was one of those foam sanding blocks (the same 150 grit one I used to sand the surface before I started) with the paper wrapped around it. I used 600, then 800, then 1500 (2 coats between each).

You will probably have to experiment with the correct mixture of mineral spirits. I started off trying to measure, but it was a pain to try to measure very small amounts (like under 2 oz total) since I was doing a small area. In the end, I just had a yogurt container where I mixed the paint and spirits, and got it a lot thinner than it comes out of the can, but not watery. Then I'd pour it into the paint tray, and what was left I'd put back in the yogurt container (w/lid of course) where I'd mix the next batch in with the old batch. Very little waste with that process..