I am a sailor and loved my 7-day stay on this little boat. The Marina is modern and has clean ablution facilities. The boat is in a secure area only accessible with a keycard. I thoroughly enjoyed hanging around and eating in the numerous little neighbourhood tavernas in the Afurada area behind the Marina.
The boat is perfect for two people - three may be a bit of a stretch, and is excellent value for money.
The central Gaia area is about a 3 km walk along a (mostly) promenade from the Marina. A busstop to travel into central Porto is about 800m up a hill behind the Marina.
Consider renting a bicycle when you stay here. There are dedicated cycle paths towards the mouth of the Douro on the Gaia side, and you can cycle into central Gaia.