Josh, I am not a professional painter so maybe I should not contribute here but...... If you are going to seal I agree that 400 should be fine enough and also believe that you should be fine to wet sand it. I am sure you started out with Epoxy on your bare metal so you have protection from rust there.
Hopefully Ray, Henry, Brian or one of the true experts will join in. You could also check with Barry K at SPI. He would be more than happy to give you sound advice if you are in a hurry.