Suggestions for a new team/playing against characters that always seem to blow me up?

I started playing fighting games 2 years ago with SF4, but I didn't take it seriously until I bought UMvC3. I bought a fight stick, the strategy guide for frame data info, and I've been following streams heavily since I started, including watching all of the EVO streams this last weekend. I have switched teams frequently, but my current team is Captain America/Frank/Doctor Strange. I also know Deadpool, Vergil, Nova, and Spencer somewhat well. I am looking for suggestions on how to run my current team well, but mostly I am looking for tips on a few characters that blow me up.

I have awful trouble against Ammy. I know that her basic combo string involves about 8 hits of forward-H, but I seem to have trouble predicting when to answer to this attack string. Is it better to wait until the string ends, then call an assist and attack overhead or is something else more effective? I find this works about 50% of the time, but the other half I get hit with a happy birthday.

Doom also frustrates me. I try to block high to avoid the footdive, but it seems to connect much more often than it should, even when I feel like I am blocking in time.

Magneto, I have no idea how to block against. Any help here is appreciated.

Aside from these specific characters, I find my biggest weakness is blocking teleport mix ups. Most people try to teleport behind, but should I start blocking this direction when I suspect the behind teleport, or when I visually confirm it? I have found that almost anyone who knows good teleports is able to mix me up and kill pretty easily, and I really want to eliminate this weakness from my play.

Any help is appreciated.

TL;DR- I need help finding out how to combat teleport mixups, as well as strategies against my personal toughest enemies (Ammy, Doom, and Magneto) using my current team of Captain America, Frank, and Doctor Strange.