Now I've been looking at an Xbox 360, which seems more affordable and has more games on it that I can't play on the PS3 than the other way around (Dead Rising, Left 4 Dead, Dead Space, anything with "dead" in the title--you get the picture). About the only game I'd like to get that I can't play on the Xbox 360 is Metal Gear Solid 4. And all future games I'm interested in--RE5, Marvel UA 2, Ghostbusters--are available for both. Anyway, I'm starting to consider an Xbox since PS3 seems to not have much of a leg up and doesn't have that many exclusives.
I usually play older games (I don't like paying full price for a game since I'm buying a house in March and, frankly, I'm excited about the deal almost as much as the game

So what should I look out for if I go the Xbox 360 route? I know not to get the Arcade Console, because that's got no hard drive and almost no inclusions as far as I understand. But past that, my knowledge is minimal.
As far as I understand, unlike the PS3, I have to pay to play online with an Xbox. Since I have a lot of responsibilities, I'm more of a casual gamer, not much of an online gamer (does that make it impossible to play Left 4 Dead, btw, or can I play that solo?), so the only thing I'd do online is probably by add-ons. Do I still have to pay to access the online store?
Here are some other questions. How many USB ports are there (can I put saved games and add-ons onto my PC and copy them to DVD)? The Xbox 360 is cheaper than the PS3... but is there a reason why? What hard drive size should I buy for casual gaming? And, like the PS3, are there differences in the consoles other than the amount of hard drive space they come with? What's this notorious ring of death about?
Anyway, is the Xbox 360 a wise decision?
I may have a few more concerns or questions later (right now my one-year-old is tugging at me to go play, so I'm a bit rushed), but for now this should help me make some sort of informed decision.