Re: "Free boat" seaworthiness
jack: It's great that you are excited and have some background coming from dinghies.
Even a simple keelboat like this has a more complicated hull structure than your Holiday dinghy. Your Holiday is probably a simple 2-piece fiberglass layout with no core. You can't assume that repair work that you've done on a dinghy scales up. For this reason a basic dinghy can be restored from failure much more successfully than a sunken keelboat.
It would take a miracle for a boat to spend significant amount of time under water and not get water into the deck's core. Recoring a deck will cost you a significant amount of time and money. There isn't an easy fix here, the process involves removing one layer of the deck, inserting new core, and epoxying it all back together. I strongly suggest reading about that process before going further.
I know that you have said that the core seems solid. I will say that it takes experience to note delamination damage before it is really bad. A little water will cause a lot of damage with time though. The tapping test can produce a pretty subtle result between "good" and "delaminated".
The primary value on a 24' boat isn't the hull. It is the cushions/interior, outboard motor, and sails. Most used 24' boats sell for less than what these parts would go for on their own. It sounds like out of these items you might be getting some unknown quality used sails for free. It's really not worth it.
boats that I sail on regularly: Pearson 28-2, Rondar 505, Yankee 30, Blanchard Junior