okay, I don't know how much time you have to edit this, but I will speak as though you had forever and you may whittle the suggestions down from there. *g*
a) during dialogue, adverbs be stricken! for example, "innocently" from Aumbrio on page 1. (sagely can stay, though) Most of the time, the adverb is implied already.
b) looking at this as a paper, I'd say you've hit more than enough artistic points, with plenty of citations.
c) I don't know how easy/possible this would be to fix, but: in most of the cited passages, it sounds very textbook-y. Can you paraphrase a bit more, make the quotes sound a little more natural in someone's head or coming out of their mouth, make it a little more like--oh, when Domenico's talking about techniques, okay, he's teaching, but he's also been doing this all his life. Thus, his explanations would probably be a little more--personalized. He's talking about the painting stuff on page 3--well, psychiatrist!frost asks, "how does this make you *feel*, Domenico?"
d) going along with that--I would try to characterize a little more throughout the story. Nothing too blatant--it wouldn't take much to make it sound forced, as you're working with real people--but a little more of a personal flavor to the narrative. There's got to be a little more to experiencing Savonarola taking over Florence, for example. Also, Domenico--who is he? what's he like? he's a little bland right now, and come on, he's an *artist*, he's got to be pretty nuts, no? Aumbrio--he's pretty understated, and basic young-shy-boy right now, which could work fine, especially if Domenico was played up a little more maybe? I liked his scenes with Catarina, and Catarina in general, quite a bit.
in conclusion: the line between paper and story is a hard one to toe, and I think you've done a pret-ty good job of it! You could probably turn it in and be fine; my comments are entirely literary criticism, and nothing to the quality as a project. do whatever you have time for! and good job. kudos to you!