The workings of the Dusk Academy are simple.
There are no regular classes held here. Sometimes, the professors teach, but to attend those classes, the students need Dusk credits.
Every student would get a minimum stipend, but that would be enough to buy groceries for a month and dive into a dungeon a few times. That would be all.
If one wants more credits to attend these classes, they should be someone who has entered the academy with a higher ranking contract or enter a loot dungeon to hunt the monsters inside. The loot would be sold for credits, which then can be used to buy the available slots for the classes.
Yes, every class would only have slots. A teaching hall would have a limited number of seats for the students to sit at a time. So, only a limited number of slots would be available per teaching session.