The city is well deserved by metro and buses, but the trip is quite long to go to the university (ca. 40min from Pangrati). However, I still advise to rent an apartment in the center of Athens despite the distance, because the surroundings of the university have no interest in visiting. You can easily rent a car at Europcar (I advise using well-knowned companies) to explore the mainland.
Remember to ask for the UNIWA student card once you arrive at the university. Once received, you should subscribe to the metro/bus, it is cheap and easy to request in the metro shops. With the UNIWA student card, you have a 50% discount on every ferry to any destination, and on some historical sites ! We used this a lot ! You can book ferries on this website : https://www.ferries.gr/en/
