I've painted a couple sunfish, and I like the semi gloss better. My tips in no particular order would be:

1. This is the time to fix any cracks in the gel coat. I usually just sand them and squirt in some epoxy.
2. Sand and wipe down with acetone before the initial application.
3. Speaking of sanding, get an orbital sander. It will make your life ten times easier.
4. Wear a respirator when sanding! You will permanently fuck up your lungs if you don't. I use something like this.
5. Get a foam roller and you'll get a better coat.

real talk tho, why dont you just use a respirator with replaceable filters? they're like $20 on Amazon. https://smile.amazon.com/3M-07192-Paint-Spray-Medium/dp/B0002STR22/ref=sr_1_13?keywords=3m+respirator&qid=1583633441&sr=8-13