From Luz, we are planning to go to all the above cities but we only have approximately 6 days. Which cities should we stay in overnight and which cities should we just visit during the daytime? TIA!
Stay overnight in Evora, Coimbra and Porto.
Also, not sure about the appeal of Nazaré if not into the surfing scene. If you want a pretty fishing town, then Ericeira is much closer to Lisbon and easier to get to, and nicely combined with a visit to Mafra Palace.
(what do you mean by "from Luz"? From Lisbon?)
Evora you can do a day trip from Lisbon on the train.
Nazare, you can stop in route on your way to Porto if you rent a car. Are you skipping Sintra?
Porto you need 2 days and another 2 to do anything in the Douro Valley.