Lots of threads on this subject. I generally go cheap and use Rust Oleum Topside Primer and paint sold at Lowe's. Don't skip the primer. I did the first time, was okay but when I used the primer, much better. One quart of each is all you need for a couple of coats.
Yes, sand off big chunks with 120 then 220. sand lightly between coats. Rustoleum Topside or Interlux Brightside is what we use. We also have sprayed hull with Rustoleum, but it will not take much abuse as it is real thin.