I was actually surprised when it turned out that Gaia is another city across the bridge from Porto. But it turns out it's even better option for living. It was very close to Porto city center, the transportation is very convenient. And even if you walk, it takes minutes. We worked in the office near Clerigos church & it took less than 20 minutes of walking to get there (10 min with public transport). And the best part is that unlike in Porto, here the streets are very quiet, no cars or commotion outside at night and even during the day.
The apartment is very clean and cozy, it has all the necessities. We didn't need anything while we were living there during the week - and we cooked & ate at home and spent some evenings there. I really can't think of anything that wasn't right with the place.
And the owners are very nice & hospitable. It was a pleasure to stay here.