RE: bottom paint how much
I have used cayenne in the bottom paint for my dinghy and it does work. Used standard inflatable bottom paint one year, almost no effect. Next year added about 1 oz cayenne to a quart of same paint, maybe 6 barnacles attached over one year. Next year added some of starbrites compound X, still worked great, so the X really wasn't needed.
If you want to put an additive in, go to the paint store and get mildew preventative for house paint. It's (ta-da!) Tri-butyl tin, the good stuff that was banned from boat paints in this country.