I can actually answer a few of these as it's a little obscure where the answer is kept.
1. for this one its more speculation on my part but I believe everything involving the werewolves was an experiment by someone trying to make an army of werewolves or just figure out how genetic modification affects the werewolves. that person doing this would be the man we see talking to the werewolf after the swamp creature gets its ass whooped.
2. no one knows yet, but the teacher actually was in Northcrest I believe, when you talk to Ruben and ask about your teacher, I'm pretty sure he says he was in Northcrest for a short amount of time but left quickly. I got no idea where to, but he was in Northcrest I believe.
3. It's not spread through sex purely, it's the corrupted water and sex. the corrupted water was born from something the nameless did and was the only way originally the curse could spread, but once it took effect on a few lizard folk they started spreading it via sex as well as interactions with the corrupted water. however, the original corrupted water may have been from the corrupted lake it was not the source of corruption, that was the Nameless and he is also the one who I'm pretty sure corrupted the original lake.
4. the reason Bernard got sick is actually a little confusing to me too but the version he had actually was much milder than the one in Mythshore. the reason the one in Mythshore was so bad as we all saw was because of the booster added into a "cure" made by those people from Northcrest who ended up causing literal zombies to be born. Bernard if we had not treated him would only have died, not become a zombie since the version he had wasn't affected by the booster like the ones in Mythshore.
This is all I got, some speculation, other facts from past events and stuff characters told us. although usually quietly when we are trying to jack off since the character is either getting fucked or fucking during these dialogs lmao.