It sounds like you are breaking your Camino in several trips. For this one, you want to start in Porto and walk 15-25 km each day for about a week. You know you won't make it to Santiago this trip. You will resume where you left off on another trip. If I've got it right, I recommend:
Day 1: Porto cathedral to Matosinhos (about 12 km so a bit short but it is the first day) Walk down to the river from the cathedral and along the river to the coast, then up the coast to Matosinhos. If this is too short, you can keep going to Vila Chã, combining with the next day, which is what I did. But then it is 26 or 27 km, so a bit longer than your range. If you manage this in one day, your week will take you to the Spanish border, just over 100 km from Santiago, and you can complete the Camino on your next trip and get a Compostela.
Day 2: Matosinhos to Vila Chã (14 or 15 km), north along the seashore (Senda Litoral)
Day 3: Vila Chã to Rates (19 km), north along the Senda to Vila do Conde, then turn right once you've crossed the bridge and take the route that will connect you to the Central Route. You join the Central route at Arcos and walk a few km more to Rates.
Day 4: Rates to Barcelinhos or Barcelos (15 or 16 km) Our albergue was in Barcelinhos but we spent most of our time in Barcelos.
Day 5: Barcelinhos or Barcelos to Lugar do Corgo (about 20 km) Stay at
Casa da Fernanda, reservations necessary.
Day 6: Lugar do Corgo to Ponte de Lima (15.5 km)
You may want to stop here if you took two days to get to Vila Chã, because it is a bigger town than the next village if you need the seventh day to get back to Porto. But if you this is really day 5 and want 7 days of walking, I've included two more stages.
Day 7: Ponte de Lima to Rubiães (about 19 km). This takes you over the only really substantial hill on this camino.
Day 7 if you combined the first two: Rubiães to Tui (about 21 km). If you are headed back to Porto after your Camino, you may want to stop in Valenca, on the Portuguese side of the river. I expect transportation to Porto may be a little easier there.
I can't speak to luggage transport. I didn't use it.