I would go with one of the package deals that many manufacturers have out now. For three or four hundred you can get everything you need to get started. Take a look at PSE, Browning, and a serious look at the Parker hunter mag package. You will definetly want to get it from a pro shop. It may cost a little bit more than Cabelas or a sporting goods store but they will set it up and tune it and give you shooting instruction. Most will also give you lifetime tuning if you buy it from them. I made the mistake of getting my first one at a sporting goods store and had to learn the hard way to shoot and tune a bow or pay a pro shop to do it for me, and trust me it's very frustrating. You also might want to ask if they can set you up with a package deal of their own.
As for poundage you should be able to sit flat on the floor and pull the string straight back with no strain or lifting of the bow. Don't get hung up on speed either just make sure that you can shoot it accurately. Personally I like carbon arrows. When you start shooting good groups (touching arrows) they don't get damaged near as easily as alluminum arrows do.
Save your money and get it all at one time. That way you will get it set up right the first time and won't have to constantly add something and then have to retune it. And nothing is more frustrating than having a brand new bow sitting in your house and not being able to shoot it cause you don't have a couple of things, release, sight, arrows, rest, target.