Thank you so much for your help this far, and your warm welcome to the forum!
My question is:
How does Hermetic Sorcery interacts with a Rego or Vim Affinity?
Do the experience points from Hermetic Sorcery get multiplied by the Affinity?
Hermetic Sorcery
Major, Hermetic, Tainted
Through instruction or intuition,
the character is able to easily translate
his knowledge of sorcery into Hermetic
magic. Whenever he studies one of the
four Goetic Arts (Ablating, Binding,
Commanding, or Summoning), he also
gains half as many experience points
in Rego. Similarly, whenever he studies
a form of supernatural Lore (Dominion
Lore, Faerie Lore, Infernal Lore, or Magic
Lore) he receives half as many experience
points in Vim.
The character does not have to have
any of the Goetic Arts opened to take this
Virtue, though obviously it is twice as useful if he does.
Affinity with Art
Minor, Hermetic
Your Advancement Totals for one Hermetic Art are increased by one half, rounded up. At character creation, any experience points you put into that Art are also increased by one half (rounded up), and you may exceed the normal recommended limits. You may take this Virtue twice, for two different Arts.
Except during character creation, Affinity never multiplies experience points.
Affinity multiplies your Advancement Total.
The bonus xp from Hermetic Sorcery is not an Advancement Total, so they are not multiplied by the Affinity.
Hermetic Sorcery doesn't do anything during character creation, so how it would interact with an affinity then is somewhat irrelevant.
If you wish to houserule that Hermetic Sorcery does apply during character creation you can do so, but it is not RAW.
Affinity explicitly says that it works and how it works during character creation.
Several other bonus-xp virtues that apply when you study do not. This includes virtues like Secondary Insight, Book Learner, and Hermetic Sorcery. For many of them it is mainly because it would be too complicated to figure out how much bonus-xp you should get during char creation.
It might be worth noting that Hermetic Sorcery does interact (indirectly and after character creation) with Affinity in any of Goetic Arts and the (Supernatural Realm) Lore Abilities, as an Affinity in those increases how many xp you gain in them, and thus how many you gain in Rego or Vim.
The (Supernatural Realm) Lore Abilities are quite interesting in this regard, as you can easily create a grog "specialized" in Teaching who's pretty good at them, and quite competitive with sound Vim tractatus when teaching one-on-one even after halving.