If you decide to apply a barrier coat, read and follow the directions on the label carefully. The label says that each coat of barrier paint should be applied within a certain period of time after the previous coat, and the first coat of antifouling paint should also be applied within the same period of time. The reason is to make sure they are chemically bonded. If you don't follow that time schedule, you need to apply a primer before the first coat of antifouling. Otherwise, the antifouling might peel off. If you have any doubts, call the Interlux 800 number on the label. They have an excellent tech support line.
I assume you're planning to keep the Cal for awhile, since you're doing that much work on it. If so, I'd suggest you barrier coat it, even if it has no blisters. The hardest work is stripping off the old paint. Once that's done, applying barrier coat isn't a bad job, and it's good long-term insurance against future problems. I just had mine stripped, and will be barrier coating it this spring, as soon as the weather breaks, so I'm following my own advice.