John Brierly's books are a good reference with plenty of of maps, accommodation etc. There are lots of ways to do the camino alone or in a group, in hostels or guesthouses, with a rucksack or having your pack transfered. There are lots of different Camino routes, not just the Camino Frances. The route from Oporto is about the 200km distance.
Weather should be fine in September, many people adjust their walking time for the day to suit the weather. If it is very hot, the walking is done early in the morning before it gets too hot.
Get your walking shoes or boots now so that they will be well walked in by the time you go. If it is not important for you to get the camino 'certificate', they your 200km could start or end in a great variety of places.