I probably won't be able to make it – but wanted to point out that AirBerlin flies direct Hamburg-Porto, once daily. So perhaps someone wants to organise something where they fly together?
Booking early is probably advantageous, since fares change rapidly depending on when you book (though they may go down as well, they're probably more likely to go up). Also, planes fill up, especially at the cheaper fares.
Fares right now (18 January) are €71 for HAM-OPO on 30 Aug (11:20–15:40) and €89/€99/€109 for the flight back (16:25–22:50; fare depends on whether you fly back on the 2nd or the 3rd and which fare class you manage to get on the 3rd; the cheaper one only has 9 seats left). Add €16 fuel surcharge to the sum of the two flight prices.
There don't seem to be any return fares; you simply book two separate flights and pay the sum of the two fares.