At 1) Think the decessive word here is previous season, rather than previous matches this season. Wouldn't be too surprised if the demand was so big, that Augsburg restricted the tickets to members and people that went to their stadium a few times before.
At 2) If I'm correct with my assumption at point 1 the only member of this forums, who could possible give you a hand would be @Eco, since he's a Augsburg club member and therefore might have the an first buy option.
At 3) Personally have no experience with repurchase websites would be cautious nonetheless, as seem to remember there have been faked tickets offered on them in a few instances.