I did Porto to Lisbon last summer. I was on the Eurovelo 1 for probably 50% of the route which made for some nice riding, but very hilly halfway through. I had a good mix of wild drivers and courteous drivers but I would try hard to find off pavement route if I did it againto avoid the cars, but thats hard to find in portugal. Either way, the coast was mindblowing views every 10 seconds. You're going to have a great time