Portugal itinerary and lodging insights requested

Skip Sintra. It is crazy busy! Are you able to fly out of Porto and cut out the day of travel from Porto to Lisbon. As far as the Algarve region, Cascais is a pretty area but the beaches are better in Lagos. While I was in quarantine in Obidos my husband had a night in Coimbra. He liked it though it was pretty busy with end of University.

I I would skip Tavira at that time of year. Instead i would consider Evora on your way to Lisbon. I think your timing is otherwise good. If weather is nice you could daytrip to Cascais from Lisbon for a bit of beach, but you aren’t committed to it.
You could just do a day trip from Lisbon to Sintra, although personally I enjoyed staying overnight. It is crowded but there are a lot of great sites and if you stay over you have the town after the daytrippers leave. I suspect November will not be as busy.

I agree - try to fly out of Porto at the end as an open jaw if possible - it would save you a day.

Lisbon is huge with a variety of neighborhoods - up to you where you want to stay.

Trains work fine for most of this (didn't visit Tavira, can't help you there) - I did an itinerary from Lisbon to Porto via Coimbra, by train, a few years ago. (I day tripped to Sintra from Lisbon - very easy.) But you'll notice that in Portugal, the fast trains tend not to go right through the city center - you often have to change to another train to get to the center e.g. in Porto and Coimbra.

Porto is not nearly as big. I stayed in the Ribeira neighborhood, in a private room in a hostel about a 10 min walk from the central São Bento train station.

Coimbra is tiny. I stayed at one of the modest, cheap little hotels close to the main train station (not Coimbra B where the fast train stops). It's a quick walk from there to the center of town - very easy to walk.

Many thanks to those who responded! Super helpful! Yes, have to fly out of Lisbon. Good to hear Coimbra is small, perhaps that and Sintra are day trips. We are exploring places to stay a night or two at Silver Coast to see the beach. I appreciate the time you all took to respond, thank you!!
--Kir