I just wanted to add one thing. You mentioned that you weren't sure if you wanted to spend your miles by upgrading your flights you take for work, or for leisure travel. By obtaining top tier status, you will be getting some very good first class upgrade benefits on just about any airline. Most airlines will upgrade you to first class for free in one way or another if you hold top tier status, so don't worry about spending miles on business travel. You can save those all for leisure.

Also, don't bother getting top tier status in two airlines within the same alliance. Since CO will cover you with your Star Alliance needs, just look at OneWorld and Skyteam for your second alliance. I would still recommend AA, because they count all kinds of miles toward the lifetime million miles status, not just butt in seat miles, which will make you an elite for life. If you get an AA credit card, I could see you crossing the 2 million mark easily with the amount you will be flying.