Here's my bottom paint story. Hope it helps.
Bought a boat and didn't know what was on the bottom. I called the Interlux help line and they said to paint the bottom with Primicon because it will stick to anything and then apply bottom paint. I'm glad I didn't. Turned the boat had an old graphite bottom paint (KL990?) that is no longer available. I called Interlux back and told them what was on the bottom, and they still said Primicon would work. When I questioned that they did a little checking and found out that Primicon would not work. My boat is small, so we sanded the whole bottom to the gel coat. I'm really glad that we had to do this because now we know that the bottom of the hull is in good shape. So I would say get the soda blasting done. You'll appreciate the peace of mind.
We used the Awlgrip epoxy barrier coat followed by Pettit Horizons ablative bottom paint (in the states you can obviously use Awlgrip bottom paint, but its not licensed in Canada). Expensive, but really easy to work with. The key to the whole thing was getting a good bond between the barrier coat and the bottom paint. The first coat of bottom paint had to go on while the barrier coat was still tacky. Otherwise, we were told the bottom paint would not adhere. We were told that the perfect time to apply bottom paint was when we could leave a fingerprint in the barrier coat but no paint came off on said finger. For us on the the given day with the given weather painting in the shade, this was about 45 minutes.