painting a tunnel - HELP!!

[Fassster]

I have a 21 Cougar that I would like to have painted. The primary colour on the boat, including the "bottom", right now is black, and I don't want to change that. I do want to change the accent colours on the rest of the boat, including on the side of the sponsons, some of which will be below the waterline when the boat is in the water. I plan to keep the boat high and dry on a lift when its not in use. Here's my questions:
1) the boat presently has a very good clear-coat. I assume my painter can/must sand the existing clear with maybe 400 grit, by hand, to scuff her up?
2) can the painter sand down to the lowest portion of the side of the sponsons, leaving the "underside" of the boat unsanded and untouched, without fear of the paint peeling from the seam that will exist?
3) has anyone used House of Kolors paint for marine applications? They have some wicked pearls that I wouldn't mind using.
4) any other advice? My painter is a seasoned 35 year auto guy, but not much experience in boats.

Thanks in advance for any help.

[simplyorange]

he can go to the edge, scuff further than he is painting with 1200 grit then buff it later, you have to put the clea past the color though, kinda hard to explain by typing.you can buy pearl to mix into the first coat of clear, if you use imron clear then you can just mix it with the first coat.he paints cars so if you tell him to blend the clear under the boat, then he will know what you are talking about.