Let me first say that is quite possibly the best sexy hentai-teacher picture I've ever seen. Seriously, it is very hot.
Ivygrowth, so far, most of Mitsu-sensei looks great, but as Zaer said, we need a little more to hold over her. If she is to partake in the debauchery of St. Arcadia while likely a sex slave herself, Reina Morimoto needs leverage over her. It sounds like, however, you made mention of something like this in her background when she signed the contract. That could be a part of it, where as an employee of St. Arcadia, there is very little wiggle room to negotiate things, despite the good pay. What about something more debilitating that could be used as blackmail? You mentioned a coworker; maybe they have access to a naughty sex tape from a wild night in college, or they know of severe financial issues that would ruin her, or some other juicy details that effectively puts a collar around her neck.
Lastly, what Haibane said is pretty much true as well. We are beginning the game the first year males are inducted into the school, and the students are still predominantly female. Getting into a F/F situation is inevitable, as Reina alone would be sure to toy with her on a regular basis, and then there's the rest of the dominant students like Leona and Karen. We can, however, make your preference more towards male, as I have with Reina. Even though she is bisexual, 8/10 times she would prefer to have a man as a partner. Then she can focus on and be focused on by the males.
What do you think of all this?