OK, so all these guys here will tell you how much more qualified they are to answer your questions than me (most of them are right
) But I can help out a little.....
1. Yes, this refers to how the guys are lined up, for example: a 4-3 means there are 4 downed linemen, 3 linebackers. 3-4 is just the opposite.
2. Yeah, you pretty much nailed it. But it is a bit of an over-simplification....
3. Yes, if the ball carrier reaches the 50 yard line, then during the tackle is pushed back to the 45, they would spot the ball at the 50 due to his forward progress. However, if the same guy takes it to the 50, gets pushed back to the 40, breaks the tackle, then makes it back to the 45 and gets tackled, he's down at the 45. His forward progress doesn't apply if he breaks free from the tackle.
4. An interception during a 2-point conversion basically goes down as an incomplete pass, no opportunity for the Defense to score. (at least in the NFL, rule may be different in College. You'll find that there are a few differences in these rules.)
5. If any part of the ball is past the chain, it's a First Down. Whether it's the whole ball, or just the tip. This is why the referee spot is important, because inches matter. Or centimeters, in your case. Also why you will occasionally see a coach challenge the spot of the ball.
Hope that helps.... So you guys call it Gridiron? So then when you say football, are you referring to soccer or rugby? We will occasionally call rugby "Australian-rules Football" but not that often. And on another note, it definitely seems like the NFL's efforts to gain international notoriety and fan-dom (like the NBA) is working. They should send you guys a game. They are playing a game in Wembley in England this year, they also did it last year. I also believe they played one in Mexico City the year before that.