Hey bud, it isn't going to snap and sounds like what you're describing is totally normal for us uncut guys. I'd suggest that you go over to the male genitalia section and look at the posts on stretching the foreskin. Sounds like yours just needs a bit of work with the size of the opening and not necessarily working it to lengthen it. Let me know if you need other information, good luck!
Sounds normal to me. Nature constructed the penis to have plenty of skin left over during a full erection for "gliding". This skin gliding up and down helps prevent irritation after "prolonged use", so to speak.
As for the "band" of skin (I think of a band as a circular formation) it sounds like the opening that the head pushes through during an erection. As the other poster recommended, check out the genitalia forum.
The "frenulum" is actually a small, tough "string" that comes down from the indentation on the underside of the head. On circumsized men, this is often missing, but some circumcized men still have a frenulum, myself included. I dunno what the advantages are to having a frenulum, but after all I've put mine through, it's never snapped, so I think you're safe. :-)