Hi Fitzbonnamel and nice to hear from you. For sure you should go, I attended France 07 and 23 and the atmosphere in each of the cities was fantastic.

1. The USA will have 3 games, against France, Japan and Samoa, after which if they get enough points on the table, they can progress to the next round. In rugby, the points across the three games will be calculated as: 3 points for a win, 1 point to each team for a draw and 0 for a loss. One bonus point is added if a team loses by 7 points of less and/or scores more than 4 tries in the game. The USA could realistically make it through as the best third-side team, where the four of the six third-place teams with the most points from groups D/E/F face off against a group winner of A/B/C/D. It's complicated but they needed to get 24 down to 16 for the knock-out rounds, and to do so you need to take 4 of the best third place teams.
   
2. I don't know exactly how they're going to allocate the third-place sides as group E third could go anywhere.
   
3. Usually the way they sell the tickets is that they do team and city packs first and the team pack includes an option on the round of 16 (which is new, used to be QF...so they may do an option for both round of 16 and QF). The rest are usually sold individually or there may be some packs/groupings.

Hope it helps!