The sunfish is an excellent starting platform. Also you should be able to find some for fun only races with them (if you look probably some serious ones as well)...
The Laser is the logical incremental upgrade to the sunfish (as is a force 5), but the laser is an active racing sailing class (one of the biggest), and it has some more grown up controls. You can usually find them all day long with boat/trailer in the $1000-$2000 range, and be competitive in racing with decent work on it, and a new sail/rig plan. Oh and anyone who says you can just slip a sunfish or a laser into a pickup truck, hasn't tried (lately). They are 14 feet long, and only a 8 foot bed pickup can hold them (8 foot beds are relegated to regular cabs or older pickups, I special ordered mine as a crew cab, but I'm weird). Cartopable - sure... but get a trailer if you can. It makes things easier.
Now if you want to get something that'll keep your interest longer, you can move up to the lido (also actively raced), or a capri 14.2 (personal favorite). If you can find one, a keel Capri 14.2 (trainer), or lido 14 keel, or Capri 16.5 keel (as opposed to centerboards).. are super stable, and self-righting. These are inexpensive upgrade boats that might teach you well for the next several years, and also keep your interest. In fact if you add a trolling motor, or small 2hp these boats are great family day sailors (but not great racers).
Alright, last recommendation is a larger move-up boat which is something that'll suit you for years, but might be a steeper learning curve, would be a Precision 165, Capri 18, or Compac 16. These are all small trailerable keelboats, with most of the big-boat feel in an easily handled/trailered package. These are not racers, or even fast, but are very fun/stable trailerable boats that a family would enjoy. They all hold their value nicely, because they are at a sweet spot for trailerables.
If you find something, and the owner is available (especially in these bigger boats), have them take you out on it, and show you how to rig
Lessons? Absolutely! Books? Absolutely! ASA courses, SURE! But sailing blind works too... just use a PFD, and don't wait until it's blowing 20knots... 3-5knots is your friend for now.