I have a nutplate installation tool that I bought from Avery which saves a lot of time and frustration while drilling the nutplate holes. Charlotte held the tool while I drilled. I have a #6 and #8 tool and they are worth every cent that I paid.
I used the Dremel and stones (one for the #6 holes and one for the #40 rivet holes) that I shaped on the grinder for the 100 degree countersink. It worked great except for the noise and gelcoat dust. Wear a mask or respirator if you can't get someone to hold the shop vac close to the hole you are countersinking.
Screwing on gage to check a countersink.
Countersinking the #40 holes for riveting the nutplates.