Usually, the sores self-resolve. If you apply topical ointment to sores, make sure you do not use anything with "pain relief" as that is toxic to geese. First year breeding can be brutal to watch, until the pair figures things out. But typically, while it looks awful, the girls are not unwilling participants.
Production breeds can hatch babies in their first year, while breeds like dewlap toulouse are not fertile until 2yo. But all breeds get frisky the first spring, even if they are only 6-8 months old. My hatchery african girls showed breeding behaviors at 4 months.
As for aggression towards humans, I find the best way to establish dominance with gander is to pick him up and carry him around like a baby.
Best of luck getting through your first breeding season!