Is my Portugal itinerary too ambitious?

I won't comment on your itinerary because we all have our own pace and priorities. We spent 5 days in Lisbon and 3 in Porto plus a day driving between the two with a couple of stops and thought that worked well.. We did a daytrip to Sintra and wished we'd spent 2 days.

Where are you staying in Porto? Parking was €50/ night near where we stayed in Ribeiro. Consider not getting your car until your ready to leave. We paid €14 for Uber to the airport.

That is a lot of driving to/from Salema for a small payoff in my opinion. I am not sure you can fit in Sintra in the same day. I would cut out Salema and add extra night in Lisbon. Even then, I would find your itinerary to be too packed for my tastes; I am usually not a fan of one night stays. Good luck.

Porto>Coimbra>Lisbon are linked by high speed train.

Evora can easily be done as a day trip from Lisbon via frequent buses or trains.

So, if willing to remove Salema and Nazare, you can reduce the 1 night stops and not even need a car.
If you require a beach, can always do a day trip to Cascais from Lisbon via commuter train.

We went to Algarve and enjoyed it very much. But it is way too much trouble for one night. We stayed 3 nights.

You do not want a car in Porto.

Driving was more difficult than we expected so the idea of having an itinerary you could do by train is something to consider.

I really appreciate all your responses! They are very informative, so keep them coming please. :)