Okay first off, you'd be better off asking this in the RBA section:
Rebuildable Atomizer Systems
For your questions...
1. Not sure about dual coils...don't know WHY you would want one, but to each their own.
2. That smaller post can be used as a negative connection. Again, I can't see why you would want to use it, I'm sure there are some crazy wick/wire setups that it can be used for, but I do not know or see the need for it.
edit - May have bee wrong about the negative connection, but I've read that's what it's for...hmm.