I land in Porto at 6:25am - leaving at 7:45pm for Paris. Suggestions on making the most of my time in Porto and what time do I need to be back at the airport to check back in. Also, clue me in on transportation to and from airport to these excursions plus prices if you know them.
See Rick's list of Porto attractions as a starting point to choose a couple of highlights. Getting downtown from the airport, a taxi costs about 25 euros, or it's easy by metro, running 3 times per hour and taking 30 minutes. For metro, you must buy an Andante Card (also good on public bus). In addition to public transportation within the city, Rick says "Taxis are a good option in this hilly city. Most rides are fairly short and cost only 5 euros." You could also do a half-day bus tour, offered by several companies, departing near the central tourist office.
I don't like to go to a new, large city without some guidebook info, whether you photocopy it from Rick's book at a public library or perhaps buy a chapter online, such as Lonely Planet's PDF-format chapter for $5.
Porto is a pretty compact city center. You can easily see the center area and cathedral, then have lunch down by the river, then do a port tasting or tour on the other side of the river. Hopefully you won't have or need to lug around your luggage. Know that Porto is very hilly and has a lot of narrow, steep streets.