bill and chris-
Are you going to moor the boat? If so, you'll need the bottom paint. I wouldn't bottom paint a boat unless necessary, as it is an irreversible step.
I bottom painted by CD-22 for the California Delta, but after 2 years, moved to fresh water at Shasta Lake where it is now not necessary, as the boat can be pulled and cleaned every so many months. Wish I'd never had it painted ($1100 first time, including barrier coat).
The bottom paint type should be based on the waters you are moored in, as the the temperature, salinity, and types of organisms vary from area to area. Consult with SEVERAL local marine suppliers and shops to get a reasonable consensus.
I've never heard of a C-Dory developing blisters. The barrier coat is one or more coats of epoxy applied to prevent water penetration and blistering.
The hull must be sanded for any paint to be applied. The fear is that the sanding can allow water through the gel coat and develop blisters between it and the hull fiberglass.
If you sanded the hull yourself lightly (the commercial boys sometimes use a 3" belt sander with 80 grit and a guy on his back on a creeper who wants to get the job over with quickly), you might be able to sand it enough to get the paint to stick w/o the barrier coat. We'll have to wait and see if any of our folks have been successful with this approach. For absolute safety, the barrier coat (or as many as 3 as some outfits would like to apply) is a good insurance policy.
The epoxy usually serves as the primer coat to apply the bottom paint to, unless the paint chosen has special requirements or you're interested in fairing the bottom and/or hiding any deep sanding scratches. Fairing a sailboat hull for racing takes on new dimensions in this area!!!
Are you planning on doing the work yourself?
Read the discussion of bottom paints on the West Marine Advisor as a start in developing further understanding of this subject.
Also, if you're not going to be mooring in salt water for extended periods, there are some other coatings that can be applied to prevent some types of marine growth w/o disturbing the original hull finish!
Got to go to the lake now that all the weekend crazies are gone!! Joe.