First solo trip - Portugal to Spain

"I obviously want to see/do as much as feasibly possible, but don't want to overplan and end up stressing myself out trying to get to and from each place. "

Then you need to cut your number of destinations in half, and limit yourself to one country, or else have a much longer trip.

Before you get attached to any of your destinations, look at transit links between them. You'll quickly discover the following:

1) Transit links between Spain and Portugal are surprisingly skimpy. There are a very few trains (often at odd hours), some buses, and flights. It can take much of a day to go between the two countries, door to door.

2) The Basque country is not close to other destinations in Spain. Links from Portugal are lousy, and even from other places in Spain like Madrid, you're again looking at a good part of a day by train or bus. I see that the train from Pamplona to Madrid is under four hours, so that's fine. but getting from Porto to San Sebastian will not be fast or easy.

I'm not trying to be negative - I just want you to have a good trip, not one spent on long bus rides or making difficult flight connections.

A great way to start to find connection options is the website Rome2Rio: https://www.rome2rio.com/. However, it's just a start; you then have to go to the website of the airline, bus line, train company, etc, and confirm all times and prices. I do find it handy to get a "heads up" about possibly difficult connections.

Alexandra:
Was your plan to visit the places you note in the order you noted? Based on the comments you received (above), I also think you should shrink your itinerary (or extend you time). My wife and I will be in Spain and Portugal in late October and we found exactly the "monkey wrench" noted in the prior post in getting from Spain to Portugal (or in your case from Portugal to Spain). This problem resulted in us re-arranging our itinerary. Based on our experience (we're going in the opposite direction from you), I offer a possible suggestion that works pretty well getting from one place to another efficiently and without a car.

Assuming your flight arrives in Lisbon, stay in Lisbon the night you arrive, plus three additional nights (perhaps a day trip to Sintra). The next day fly to Seville, spend the night and two more days and nights. The next day will be 7th day (after the day you arrive), take the train to Granada (this will take a while as Granada is not on the high-speed railway corridor), spend the night and the next day in Granada. The next day (9th day after you arrive) take the train to Cordoba; spend the balance of this day, plus another full day and night in Cordoba. The next day (the 11th after you arrive), take the high-speed train to Madrid. Spend the night plus three days and nights, then fly home from Madrid (if this is your departure point). While in Madrid, make a day trip to Toledo.

If you fly home on the 14th day, then the above itinerary would have to be shortened by a day; I'd suggest dropping Cordoba and heading from Granada to Madrid.

Pardon me if I've been too aggressive in modifying your itinerary. One of our goals in all of our planning is to minimize travel time and the complexity that accompanies changing modes of transportation. We've found transportation from place to place is the biggest source of stress.

Speaking of stress, you mentioned "overplanning" and "stressing" yourself. Most of the itinerary noted herein is relatively stress free. I'd suggest you book your lodging, just for the peace of mind of knowing you'll have a place to sleep each night, but otherwise not a lot of additional planning and stress. Oh yes, there is one exception; if you do go to Granada, pre-purchase admission to the Alhambra.
Jon

Have a great, stress-free time.

Sorry, what you're proposing is not realistic.

Planning on 14 days total...

Do you mean 14 full days there, not including your arrival or departure days? Or 14 days for your entire trip, which would mean about 11 full, usable days on the ground (assuming you're coming from someplace far away, like North America).

Harold makes good points above. Also keep in mind that every time you pick yourself up and move to a new location, you burn half a day (at best) to a full day (often unavoidable). So you do not have many days to waste.

With the amount of time you have, I'd suggest need to pick no more than 3 places. Choose Spain or Portugal, not both.