A lot of good questions, and the answer is 42.
About the confusing parts, the rules are now updated. Thanks for the keen observations!
Q: What happens if someone plays 12 games before the tournament ends? Are they allowed to start over?
A: While we don't expect this to happen in Single Elimination, if it happens, the oldest used element becomes allowed after each game.
Q: What about decks that originally had sideboard? Do they have to be played as they were, without any changes?
A: Those decks should be played with the sideboard, without any changes.