9 nights / 10 days in Portugal

pjs1016 - You can organize the itinerary like this:

Porto - 3 Nights

Douro Valley - 1 Night (Stay in the town of Lamego)

Coimbra - 2 Nights (Day trip to Obidos)

Lisbon - 3 Nights (Day trip to Sintra or Evora)

Welcome

Caveat- I have not been to Portugal yet but am in the process of planning a 24 night trip for May 2020 so am familiar with the locations/drive times you have in your itinerary.

Do you have lodgings booked already?

Your itinerary is an awful lot of time driving to/from locations but not much time actually IN the location. One night stays are simply not our thing as it leaves so little time to enjoy whatever town we are staying in. I would try to combine a bit and probably drop a few things.

From Regua to Aveiro is probably going to be close to a 2 hour drive- so let's say you get there by 10-11- spend 2 hours- allowing time to find parking, walk the town, get out of town- is it worth it? Probably not- although I do think Averio looks inviting for a visit but if I only had 2 hours I'd skip it.
From Aveiro to Coimbra is probably 1.5 hours- again allow for traffic, parking, etc. So you leave Averio at let's say 1 pm- you arrive in Coimbra at 3 (by the time you actually park and get INTO the town- not much time to actually see or do anything since you want to leave there and head to Figueira to spend the night.
Then you are leaving again in the am for Nazare/Obidos. Most here say Nazare is skippable and Obidios only needs a few hours at most- not really necessary to spend the night.
Then to Sintra - let's say arrive by 10 again if you get up and going early! where having a car will be a headache. Leaves you very little time to visit the sights- then to Lisbon that night and if you plan to turn in car this night most rental agencies will be closed by 7- maybe not the airport location)
3 nights Lisbon is ok.

Anyway- I would try to combine some nights to avoid so many 1 night stays- enjoy where you are- what you don't see you won't know what you missed! When you get home you can begin planning your 2nd visit to Portugal ;)

Porto 3 nights - assuming you are flying overnight from US so Day 1 is a jet lag day- maybe do a day trip to Douro- boat cruise- if Douro is super important.
Get car drive to Coimbra- 2 nights- stop in Aveiro for lunch on your way-
(or skip Aveiro and drive up the Douro - long day then to Coimbra for 2 nights)
Drive to Lisbon-4 nights stopping in Foz and Obidos for a few hours each. Visit Sintra as a long day trip from Lisbon.

I like to use rome2rio.com to familiarize myself with transpo options and time/distance but always add time to whatever it says

Hope that helps and hope others more familiar with your route jump in!

ETA: AH! I see RJean gives almost same advice.
We are actually staying in Lamego next May

Thank you both for the quick reply. We are going to consider consolidating a few of the nights and staying in Coimbra vs jumping around so much. I'll review further and appreciate your comments - and anyone else's comments.

Just to clarify, 9 nights is only 8.5 days. The day you arrive is night 1. You might have half of this first day for sights, after getting from the airport to your lodging, checking in, etc. The next morning begins nights 2 through 8. So now you have 8 nights and 8 full days left
. The morning after your last night, night 9, will probably be spent at breakfast, checking out, and getting to the airport. A good way to plan is by nights, keeping in mind the time to get from and to the airport. So 8.5 days is not as much fun as 10 days but might be more realistic.

I stayed in a quinta just outside Regua in the Douro Valley, right on the river and in the middle of the vineyards. Loved it. I stopped briefly in Lamego (not on the river AFAIK) on my way south, then in Viseu which I liked much better.

I didn't get to Figueira da Foz. It's probably much less touristy than Nazare (which turned me off). Plan to visit Obidos first thing in the morning or mid to late afternoon. I was the in the middle of the day (late May on a Saturday) and it was full of tourist groups, mostly foreign, a couple Portuguese.

I would stay in Coimbra, many more hotel and restaurant choices, easier to drive in and out of. You need more than a couple hours to see Coimbra. I enjoyed Aveiro (spent a full day and a night there) but my trip was more than twice as long as yours. With such a short time, I'd skip it.

You don't mention either Batalha or Alcobaca, two stunning (and very different ) Gothic monasteries.

I spent 3 nights in Sintra and I think having a car there would be a nightmare, even more so if you are only spending a few hours there. If it's high on your list, see it on a day trip from Lisbon.

Lastly do NOT plan to drive into Lisbon on a weekday morning. Inbound traffic is horrible and it can easily add 2 hours to your travel time. I'd also recommend not trying to drop your luggage off at your hotel before returning the car. Driving in Lisbon at any time of day is slow. It's better to drop at the train station, or even the airport and take a taxi to your hotel, if you don't think you can manage on the metro.