A few thoughts....
* Avoid e-Bay as you will have no idea of what you bought until it is in your hands.
* Find someone locally who is skilled in wood cutting to show you the ropes.
* Don't be afraid to ask questions (it might just save your life)
* Before buying a saw, why not rent a couple of different ones? You can try out a couple of brands and/or sizes before you make the plunge of buying a saw.
* Be sure to buy (and use) PPE (Personal Protection Equipment). At a minimum chaps, helmet, eye and ear protection. Others may suggest steel towed boots and gel gloves.
* Start small and work up. Learn to use the saw bucking before you start trying to drop large trees.
* If you buy a used saw, do it locally and take someone with you who knows what to look for (scored piston, bad AV mounts, worn sprocket/bar/chain, etc. However, the Trading Post here often has decent deals.
Remember, you probably need to be working a year or two in advance (depending on what you are cutting) in order to have seasoned wood when you need it.