Is it permissible for an employee of the Islamic University to take out a murabaha loan to purchase housing, given that he is a merchant? And is it permissible for him to buy devices at one price and sell them at another, knowing that he is responsible for their maintenance?

If by Murabaha you mean interest on the principal amount, then this is the prohibited usury (riba). However, if you mean the permissible Murabaha (where the bank buys the house and then sells it to you), then there is no harm in it. Regarding buying devices and selling them to friends, it is permissible for you to increase the price on them if you bought them for your own account and then sell them. However, if they appointed you as an agent to buy them, it is not permissible for you to charge them more than what you paid for them; rather, you can request a fee for the service.