You can do Sintra as a day trip from Lisbon, no need for an overnight. I would take the night from Nazare for Lisbon or Coimbra, but I'm not a beach person.

You can take the train from Lisbon to Coimbra and then take it from Coimbra to Porto.

You can get to Nazaré by train on the Oeste railroad line, that links Lisbon to Figueira da Foz, getting off in Valado dos Frades (6 km from Nazaré). For buses, check Rede de Expressos (www.rede-expressos.pt).

As noted, Sintra is a good day (by train) trip from Lisbon.

And yes, Evora is worth an overnight.

Thanks to you both for your feedback. I tried to extend my stay in Lisbon after reading your comments, but the flat is booked, so I'm stuck moving on. I thought I'd need at least three full days in Lisbon to see the sights, so I was hesitant to devote a day of that to Sintra.
Robert, you said Evora was worth an overnight. If it's a choice between two nights in Evora or two nights in Sintra , what would you choose?
Thanks again for your help.

For me, no question, Evora. With two night there are many towns to visit if you so chose, either north or south of Evora.

All within easy reach.

But we have had a car both times in Evora, so not sure about bus or train possibilities.

As iris1745 says, two nights in Evora. Sintra is interesting, but I would have a hard time staying for longer than a day-trip from Lisbon.

You may be interested in reading Maribel's newsletter that included a visit to Evora (maribelsguides.com/mg_newsletters.html)

Thanks, Iris and Robert, for your help. Good advice.
Robert, that link didn't work for me. I went on Maribel's site but could find nothing on Evora, unfortunately. But thank you for reminding me about her. I'll refer to her guides for Bilbao and San Sebastian.
Cheers.

We enjoyed overnights in Evora, Nazarre, Coimbra and Porto from your list ( we stopped more places to the north of Porto as well). Evora was a favorite, only stayed one night, wished we'd had more time there.We did Sintra as a day trip which was perfect from Lisbon. We rented a car and suggest you may find it helpful to consider doing the same.

Thanks, Happy Traveller. I thought about a car, but I thought I'd give us a break and stick to trains for Portugal. We'll be picking up a car in Vigo and exploring the coast to Bilbao that way.
Thanks for the vote of confidence for our location choices. Great to hear.