Now, I'm not sure if I understand this too well. When generating characters, can a magus have supernatural abilities without any problems?
Also, can magi of other houses have the new virtues in the Ex Misc part of Societas? For instance, could a Bjornaer magus have Mythic Herbalism?
Yes. There is nothing to prevent a magus from having Supernatural Abilities. The only time a problem arises is when a magus discovers a potential apprentice with multiple Supernatural Abilities, then the master's InVi score must be sufficiently high to open the character's Gift. Assuming the potential apprentice has relatively low scores and only a couple of Abilities, it's not a problem for most advanced magi. Learning new Abilities after your Arts are opened, that's going to create problems and may be what is creating the concern/confusion.
Definitely yes. Anyone can take Mythic Herbalism. The description mentions several times that people outside of the Pharmacoepian tradition have the Ability. I don't recall whether all of the other traditions explicitly state this possibility, but there is nothing I can think of to stop someone outside of the Columbae or Donatores, for example, from having Warding or Banishing. I know the Banishing example, specifically addresses this possibility.
Cool, thanks. That clears it up a bit.