If this is your first bow, I strongly suggest going to a good pro shop, maybe a few, and ask them these same questions and try some different bows out. Also give them a spending limit, bows run the full range from affordable to pretty darn expensive. Also keep in mind you will not just be buying a bow. You will need the bow, a rest, sights, maybe a stabilizer, arrows, tips and most likely a release. Not to mention a target to shoot into. All this stuff adds up pretty quick and may equal what you spent on the bow alone. My first bow was a Darton Yukon, it was a mid priced bow at the time and the sticker went for $350 just for the bow. By the time I was done I had spent close to $600, and I was not getting expensive accessories or anything. A cheap prong rest, 30 dollars sights, inexpensive release and the such. And that was without a target or stabilizer. I'm telling you, it adds up and take it into account ahead of time.
As far different bows, everyone has a preference to brand and type, but it's really just a preference in the end. Pretty much every bow on the market shoots well, it just depends on what you want to do with it and how it fits you. What I think is a great bow for me, someone else might not like at all. It's a very individual thing. Some bows are known for certian things however. Like mathews are very shock free and smooth when you shoot them. Bowtechs on the other hand are very effecient and have very good speeds.
Being adjustable for draw length is another issue. Some bows are better than others. Some are adjustable by using a different cam for a speicific draw length range, having a post type adjustment for for each inch or so in that range, lets say 4 inches or so. These are very versatile bows with lots of adjustment for an archer. Other bows are adjustable using a module system. You swap out a module on the cam to change your draw length by an inch or half an inch in some cases. Other bows use a module system, with small range of adjustment for fine tuning. Like a 27 inch module and a way to fine tune it up and down say maybe half an inch or so in either direction. Other bows, like Mathews for instance require a different cam to change your draw length and offer no adjustment at all other than tweaking your string and cable. The plus side is you can't get these bow over the net, you have to go to a dealer. This insures that the bow will fit you to begin with. And if it needs to be changed to fine tune it the dealer can swap out the cam, most likely at no charge to you if you bought the bow from them. Same thing goes for the bows that take modules for the most part.
Here is a link that shows all the parts on a bow and what they do and different aspects of different designs. It also has a list comparing different bows for speed and forgiveness.
http://www.huntersfriend.com/bowselection.htm
I'm going to say it again, I strongly suggest that if this is your first bow, don't order one off the net to save a few bucks. Go to a good shop that will let you try different bows at different draw weights so you can see what you like and what fits you. More important than the type of bow you get, is making sure that bow fits you properly.
If you want us to suggest some bows that are good bargains for the beginner archer, ask and I'm sure you will get some opinions, or do a search, it's a topic that comes up often.
Good luck, and feel free to ask more questions as they arise.
Paul