It was a very nice stay.
Luis was a very thoughtful host and his flat was tidy and you'll find everything you can ask for. The City centre is easily reached by metro, bus or taxi (approx. 7€) and there are all kind of shops nearby. We recommend the bakery that is close-by, (it's near to the bus station) for sweet delights and good bread.
If you come to Porto in wintertime don't forget to bring some warm clothes, because it can become quite chilly in the flat, even with the two heaters. Nonetheless we had a wonderful time.
A big thanks also to his parents for picking us up at the metro and driving us to the flat on the first day. We would come back!