So, Question 1:
THE vs A(N) - my understanding is that "THE" represents a specific thing (not a specific KNOWN thing) - so I used it like THE sorcerer, THIS one, in this story. Not just any sorcerer. Why is that wrong? I mean, obviously, you don't know YET who it is, but it is THE sorcerer.
The question here is not actually a grammar question, but rather concerns clarity in writing. Grammatically, there is nothing inherently wrong with the sentence that raised the comment, but presentation wise, it is jarring.
As well, the problem here is not an English specific problem, because if it was in Spanish, I would see the same jarring discordant note in the sentence.
The line, "
PCs need to stop a mad sorcerer/fey warlock Atlantes and free the innocent friar," would read more clearly if it was, "
The PCs need to stop a mad sorcerer/fey warlock Atlantes and free an innocent friar." The initial, "
the," in the edited sentence makes it clear that we are not concerned with just any old PCs, but specifically the PCs who are running through the adventure. This is a minor point. The second edit is more important for the smooth flow of presentation. By having "
the friar," when presenting an initial overview of the world, you make it sound like there is only one friar at all, or a least only one who is innocent. By replacing, "
the," with "
an," you make it clear that there is more than one friar in the world, but that there is one in particular that the PCs will be interested in, that he is falsely accused and needs to be free.
Later, in the presentation, when the particular friar is introduced something like, "T
he monks at the monastery assigned one of their own, brother Matthias to investigate." After, he can then be, "friar Matthias," "Matthias," "the investigating monk," or even later, "the falsely accused friar."