First, I own an 83 C22 and would never consider such a thing. But as you said, you know the risk, how tender those boats are, and how they are not the best at righting after a knockdown.
That being said, to get to your questions...
Kind of depends on the year of the boat. Many good suggestions so far and I agree with others the most important thing is making her as water tight as possible.
- Thru transom scruppers
- Locking companion way boards (at least the bottom one)
- Sealing lazarettes and bow hatch
- Manual and auto bildge pumps
- Everything tied down
- Backing plates everywhere, turnbuckles and cable new.
etc.
Also, there were several modifications over the years, the most important in early models (dont remember the exact year) was reinforcement of the forward stay. The older ones are known for pulling loose with large or extremely loaded headsails. Check in the anchor rope locker and there should be a connection to your bow tow eye.
Make sure your keel hardware is in top shape before you go. While I doubt you will be raising and lowering it much, the pivot pin hole in the keel tends to become elongated and, in addition to the annoying "banging sound", could pull loose from the hull hangers under large lateral forces. Also, about the only keel work you can do when in the water is replacing the winch cable. Any other work and you must lift the boat.
Check the spreaders. If your spreader to mast connectors are cast aluminum replace them with stainless steel as the cast aluminum are known to break without notice under load.
Those are the things I personally know about with factory boats not related to rigging for single handing, adding non-factory upgrades, etc. I'll edit if I think of any others, since my log is at home and well... I'm reading sailing posts from work.
Good luck,
MZr7