Re: bottom paint
IIRC the paint you speak of, (sacrificial paint) has heavy metals in it.
Copper or if it's old, some lead.
That's why it works, some critter grabs on to something that comes off.
If you want to do something harder, your going to be required that the old paint be removed...completely.
I say let it wear off in time, then at some point get out the Tyvec suit, respirator, goggles and vac assisted sander.
That's what they do in the boat yard for that mess, not one of the favorite jobs. You come out all blue.
If you keep the boat on the trailer, I would go with a gel-coat to match the rest of the boat.
That might run into some$$$$$$$$ though.
Good luck, the more you use your boat/wash/rinse/repeat, the less you have to sand!
LCjeff