Hi Jan/eldarin, welcome!
IonianD will surely give you the guidelines for characters, most everything is here.
Not really grokking this Flaw, but you could certainly make a Greater Malediction and flesh it out more. If you look at all the characters participating, all Flaws and Virtues are more or less from Core/Houses of Hermes, so not really sure if such a Hermetic Flaw would be appropriate.
Taking a Major Virtue to completely offset a Major Flaw does not seem right.
As for House, you do you! From a Covenant perspective, we lack experts in Animal or Herbam, who would be most welcome for money making schemes, in Mentem (Annastaj apparently is), Imaginem, Aquam, well, most everything! 