All the abundant pilgrim infrastructure awaits for you on the official route which is Central from Lisbon to Porto. It goes via Santarem and Tomar. I walked there at the very end of Oct, out of season, there were between 2 and 9 people on the given day, so we even formed a Camino family and walked together most of the way. If you decide to go by the coast you most probably need a GPS as I wouldn't rely on the yellow arrows there. I enquired about Camino in Sintra when I was there 2 years ago, no one knew about it in the info centre although it seems to pass through town. Accommodation will be in the pensions and holstels as are no albergues there on the way. I walked 10 days Santaren - Porto + 9 days Porto-Santiago on the Central. If you have 2 weeks you could try starting in Coimbra or Agueda. Bom Caminho!