Here are the basic types:
All in Ones- like a disposable, but not
Prefold- old style, requires pins (or snappi), and a cover
Contours- a little bit more shaped than prefold, but still requires pins and cover
Fitted- requires a cover and sometimes pins, but has elastic around the legs and fits more like a 'sposie
Pocket- can be waterproof or not (so need cover or not), and usually fits like a 'sposie. The absorbant bit is separate and 1 or more can be stuffed in the pocket to customize absorbancy and taken out for washing and drying which makes drying faster. You cannot take the insert out and put in another one without washing it bc the inside layer next to the baby's skin will be all wet and dirty.
In general, prefolds are cheapest, and AIOs most expensive. They are cheap and easy to make yourself, so if you sew at all you might want to try that. Or consider buying some from WAHMs. The number of diapers you need depends largely on how often you wash and how often your child goes. You probably need to change a little more often w/cloth than w/'sposies, so if you change 6 times a day, that would probably be the minimum you would need. You might want to try one of each of a few different types to see what you like best before spending a lot. There are some websites that sell "trial packs" too. Also, cds have resale value. Good luck. HTH