Check out the classified section here. You can buy a much better bow used, some barely used, than you can a new bow. I agree with the weight suggestions. The length depends on how you will use the bow. If you do decide to hunt, say whitetails, and you plan to use either a tree stand or a pop-up blind, you may want to keep the length down a bit. I wouldn't go over 62" for tree stands and 58-60" is ideal for blinds.
Longer bows tend to have less finger pinch and some feel they are more forgiving. I love my 58" Kanati's for all around hunting. My Mahaska works from a tree stand, but is kind of a pain in my blind. The Kanati's win there. They also have great speed and handle heavy arrows very well for their draw weight.
Don't worry about it too much at this point. Buy a good quality bow of 40-45# draw. Shoot it, working on form and accuracy. My guess is, by the time you are ready to hunt, you will be addicted like the rest of us and you will add to your collection.