ok, wow, so I had a bunch of work to do over the last couple weeks and dropped off the radar for a bit, I didn't think to look back at this forum.
In response to ZombieLenin, in terms of setting stuff, I played DoW, so from that i have a little knowledge, and recently I started the tabletop game, but I only have a couple codexes, so my knowledge is limited. However. I also have a friend who is a 40k fanatic. He is honestly a walking 40k encyclopedia, I mentioned the Rogue Trader RPG, unaware that they were more than a title for a book, and he gave me a speech on who they were, what they did, and their history in the tabletop game. So I have access to the information if I need help with setting/story.
I did get OW, and partially because of the setting, I liked the idea that the players aren't super soldiers who can take down armies but regulars (as close to as possible in 40k) fighting in a horrifiic war. The second, probably more important reason was rules. I am a relatively new GM, and I was looking for a system that wasn't cluttered and bulky within the 40k universe, and from what most people around the forums said this system tended to be the most clean cut. This doesn't mean I don't plan to get any of the other books. On the contrary I do plan to get RT at the very least, the setting of that one is really appealing to me. Dark Heresy and Deathwatch I also am looking into, but right now I am a college student with a limited amount of funds, and at this time am only willing to put the money and time into one book.
What it really hindered on was as a new GM I wanted a rulebook that wasn't overly complicated, I tend to lose motivation to run a game if that happens. I've run a session of a RPG, very little experience, and OW fit the bill in terms of ease of use primarily. I also liked the characters/setting, maybe not as much as RT but still very interested in it. I definitely plan to get RT in the future, but for now I will start with OW.
Again I was suprised by the amount of replies after I had disappeared for awhile, but thanks everybody for the feedback! It answered all of my questions.