Focus on the first three. Make sure after you beat each one you do all the side quests so you can take the good stuff with you to the next game. This is going to take you a bit and is going to let you have more time to get the fourth game.
I know about this already, but thanks.

Watching Let's Plays is fun, and is what sparked me to search for them anyway because I'd almost forgotten about it.
While doing a flyer run for TnT and May 8th, I asked at the 71st Game Exchange what they had -
Outbreak for 19,99, Infection for 14, and GU Rebirth for 18, but didn't have the original case.
There is also a NEW Game Exchange on 21st and Sheridan, but they had closed by the time I was doing my runs.
I'd call around man, seems like they are out there, definitely at GE yesterday, the one off 71st across from the mall.
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Thanks. I'll definitely do that, especially when I actually get the money I need to buy the games, which I should get shortly.
I figured it'd be best to ask here first, since I don't frequent game shops all that often in the first place.