You can't expect instant success.
UGC is a good place to start because it's free, if you have people quit or flake out, it's not a big deal because you don't have anything invested into it besides your time. And if you'd be playing tf2 anyways, you haven't lost anything. But you have to stay committed to putting yourself in the proper division and consistently trying to get better.
I think a flaw in the way we've done things over at UGC is that some teams are content to just hang around in steel, think they're good and move on and then they get surprised in ESEA and die.
As long as you're committed to getting better it will happen. My old team started in UGC, won UGC, and moved into open and then eeked its way into IM - as long as you're committed it's ok.
Yes, you will get rolled in open, in fact, you'll get rolled occasionally in every league unless you're a member of Mix^, Bp, etc.
Main would be sweet, but it wont happen because IM teams have an extremely short life expectancy.