It's great you are asking these questions and educating yourself about what to expect, but before you go any further you really need get that first class medical now, not just rely on what your AME says. I have seen it happen to students, they invest time and money to fly, and then find out they can't get a first class medical. As far as how much time to get to the airlines who knows, especially 3 to 4 years from now when you are finishing school.