I would check the train an bus connections to answer the transportation questions. Rick's book would also have great information about this. We rented a car on our 2008 trip, but we also included a lot of places more out of the way like Nazare, Tomar, Evora (on a different train line from the north/south), and even made it to Alcobaqa and Marvao. One night stays are tough, I try to avoid them. Definitely finish in Lisbon, and yes I would give it four days, especially if you are going to include a day trip to Sintra. The Gulbenkian Museum and Belem are highlights, and don't forget to ride the scenic trams! Sintra, it would be so great to stay overnight as we did. It really is a magical place. Our highlights for Portugal were Lisbon, Sintra, Nazare, Obidos (day trip from Nazare), would fill eight days. Second tier highlights Porto, Evora, Coimbra. There were no lowlights, none! Lisbon is one of the most underrated cities that I have visited in Europe, and I've been to plenty. Portugal, once of the most underrated countries. Spend a little more for hotels as the standards are a little lower there that most countries in Europe. We were there in September and the weather was sublime, like southern California. The golden light at Nazare on the beach at sunset was absolute magic. You are making me wish I had gone back to Portugal instead of Italy on my recent solo trip!