Welcome to FT! You asked a very clear series of questions that should provide you with a wide variety of answers! Hope you stick around, learn what is offered here and share your experiences as you learn the tricks of the trade.

Since others have addressed alliances and the like, let me talk a bit about airline status.

Status is granted by an airline for a certain amount of flight activity over a period of time. US based carriers tend to grant status on miles flown per year. Other airlines base status on calculations of miles flown and cost of the ticket. The beauty of status is if you earn status on one carrier in an alliance, you have reciprocal benefits with the others. What does that mean? If you have Platinum status on American, you get perks on Qantas, Cathay Pacific, Japan Airlines and the other oneworld carriers. For example since becoming an Platinum (>50K miles flown) and later an Executive Platinum on American (>100K miles flown this year) I have enjoyed the BA Lounges, priority check-in and even a long haul upgrade!

Some carriers may have lower qualification standards and allow longer time to requalify. It seems many around here are fond of Asiana for that reason. Fly on another Star Alliance carrier, credit miles on Asiana and you can earn status quickly and have 2 years to requalify! (If I understand things right)

I suggest you poke around on FT and on the Flyerguide wiki to gain an understanding of what options are out there.

It will be a bit overwhelming at first, but a little bit of effort up front can reap huge rewards over a matter of a couple years. As a testimony to what can be learned here, last year I had no status and 19K miles with AA. I knew I was going to fly a lot (for me) this year, expecting 50K miles and I wanted to maximize my bennies. I wound up flying a lot more than 50K and am now sitting on 300K redeemable miles, have been upgraded on 5 longhauls, earned 8 system wide upgrades and have used 2 for me and 3 more for my family. I've enjoyed oneworld lounges in the US (x5), Britain (x2), South Africa and Spain. Sunday I will be checking out the lounges at London-Gatwick) I no longer stand in long lines and when flying coach I sit in exit rows. I am among the first to board thus almost guaranteeing overhead bin space. When the inevitable goes wrong, I have access to a special line dedicated to helping elite members.

So I urge you look around, ask questions, and learn how to make flying a much more pleasant experience!