As a portuguese, welcome to my country. October is a good option, as all the tourist crowds are gone... I would reconsider not going to Lisbon and Porto, as these are two of the best towns in Europe...
North of Lisbon, it depends how far you go. Around Lisbon there are nice spots (Cascais, Sintra). Further north along the coast, there is Nazaré, Sao Martinho do Porto, Aveiro, all nice. Inland to the mountains there is the Geres Natural reserve; in north Alentejo, one of my favourite places is Marvao and Castelo de Vide. So many places to go!
I invite you to visit my website for photos of these places, perhaps they will give a flavour of what to expect: www.paulobizarro.com