A few thoughts:
Plenty of people have made passages in pocket cruisers. In fact, someone just started a pocket cruiser thread, listing all kinds of tough little boats. My only question about your
boat, is the swing keel. How much ballast is in that keel? How much ballast does a Sea Witch have? Hopefully this is not a very tender boat. It would be interesting to know what the Stability Index is for this boat.
It's good that you've upgraded the standing rigging, but this puts more weight aloft, and if the boat is already tender, you have exacerbated this a little bit. In the ocean, this can be a Bad Thing.
I agree, that a lot of dehydrated food can dent your water supply. Canned foods are heavier and take up more room, but you're carrying fluids in the cans. There are also military type MRE's (Meal Ready to Eat) that are not dehydrated, yet also not packed full of water, and stow more easily than canned foods. They are also self-heating. Check with your local hiking/backpacking supplier, or online.
Water: I recommend either collapsible water bladders or the 2.5 gallon jugs with a spout instead of 1 gallon jugs. The bladders and 2.5 gallon jugs can be set on any horizontal surface with the spout open to provide "running" water. You can't do that with a gallon jug, plus gallon jugs will cause more plastic waste, and don't compress down as easily when they're empty.
You probably already know this, but stow all of your heavy foods and fluids down as low in the boat as possible so that it will perform as additional ballast instead of a hindrence, up high, making the boat more tender.
2 people on a 20 footer, plus provisions... whew, that's going to be tight.
Good luck, post pictures, start a blog or something!