SJ24 is a pretty stable, average built boat... the fin keel will provide a pretty stable ride and the performance is also better than other 24s of the same vintage. Yes the SJ suffers some from the IOR rules, but luckily isn't an extreme IOR rule beater type boat.
Many like to tout the great starter boat as the Catalina 22... it too has too little cockpit and more cabin than is useable for such a small boat. The real advantage of the 22 is it's ease of trailering. If trailering isn't your thing, than I submit many production keel boats, preferably fin keel, will provide a stable forgiving sailing platform that many of the lighter trailerables done... again subject to water depth and ability to sail off a slip versus a trailer.
I personally have offered up the Capri 22 as the ultimate starter boat. It has very little cabin, but a huge cockpit of almost 9 feet. It has all the grown-up sail controls, in a tiny package. They also made a standard rig, a tall, a fin, and a wing design. So depening on what your immediate needs are there is a version that works best... some don't have water problems, so the fin is good. Some need to trailer so the wing is good. Some have mostly light air and the tall rig is better.
My point is, given some parameters, the SJ, a pretty common keelboat, will have a huge following, and many people who can help point out the strong points and how to get the most out of the boat. Also with a bunch of people still sailing them, finding parts should generally be easier, and asking questions on how to maintain the boat and what problem areas to focus on should also be easy.
Now focusing back on the OP, keep in mind maintaining these older boats comes with an lot of extra expenses. Don't expect a 1976 sailboat to be up to off-shore work (and it doesnt' sound like you do) from day 1. Much of the rigging on these boats require, not only labor, but also $$ to get you up and running safely. That includes necessary safety gear.
PS: If that C&C is available it'd be way more boat if the OP is attempting to spend much time off shore. Didn't we have another person wanting to get AN SJ 24 and sail around the world. Ah yes Rimas! Sailing around the world in a San Juan 24 - Sailing Anarchy - Sailing Anarchy Forums
To the OP keep your expectations of a 40yo sailboat, er, um reasonable. The fact that poor Rimas is still alive is a miracle of epic proportions.