Your first question will likely center around your first boat. Either you have it, or you are considering getting one. Try to take a step back from that position, and consider where you are going to sail it. Most people find that sailing with others offers much more enjoyment than sailing alone. The popularity of yacht classes is a highly local phenomenon, with clubs nearby each other often sailing entirely different boats.
Most clubs have a preferred class.
Yacht racing is highly dependent on the laws of physics, and different types of boats are not close enough in performance to make it much fun on the water. There are many who just enjoy the building and sailing. After all, it was fun with that simple board and cloth. The focus on most of the information here is on racing, but that is only because racing requires almost endless rules and regulations to ensure fair competition. Don't let it turn you off.