Hi! Lisbon is amazing, very interesting town. Otherwise Porto is really nice too, smaller and perhaps cheaper... I won't go to Lagos (Algarve region) as it is very touristy, although the landscape / seaside is beautiful.

Given what you've said, your interest and time of year, I'd recommend staying in Lisbon.
Cascais is basically a suburb of Lisbon, albeit a quite expensive one.

Thank you! That's something to consider, especially since American suburbs are not my thing. But the population density of Lisbon is high. I loved the good old days in Seattle when it wasn't so crowded. Now, it's hard to visit, unless I'm downtown without a car. Haven't lived in a city for a while, but loved old Dublin and city neighborhoods in Minneapolis, Philadelphia, and Portland Oregon. Are there Lisbon city neighborhoods that don't feel awfully crowded? It sounds like it's very easy to get away from the city, but I don't want to feel like I need to get away.
The older parts of Lisbon, where you get the old world charm, are fairly crowded and, by US standards, noisy.
I would not describe Cascais as a suburb. It is a former fishing village that has grown into a nice town. It is at the far end of a commuter train that runs into downtown Lisbon, so it is easy to go into the big city, and some people who live there who commute in Lisbon daily. I am not sure when the train was built, but I think it was in the 1920s. There is a very nice, quite residential area immediately to the west of center of Cascais. This area includes a large park, and good access to many restaurants, shops, cafes, and is easy walking distance to the train station.
The downside of Cascais is that it is relatively expensive compared to some other areas. Having said that, the cost of living there is less than Portland.
My interests are fairly close to what you have expressed, and knowing the Libson area well, I would pick Cascais. Other choices would include Parade, or Carcavelos

Cascais is the best place to stay, unless you want to be at the very center of the city, which you said you don't. Only question is price, how far from the center you can afford to stay, and apartments vary in quality greatly.
That said, if you find a great apartment anywhere on the train line from Cascais to Lisbon, as well as around Parque das Nações, I would say the quality/price of the apartment would take precedence over the exact location. There is nothing wrong with Estoril or Carcavelos. There are local cafes, local shops, etc.
Also, well, just a piece of advice. Maybe stay flexible. For example, this year, spring weather in Portugal was horrifyingly bad. In 2014 it was terrible all the way up until end of March. Rain, low temperatures +14-16C, and apartments have bad heating.
Also, maybe consider other cities as well. Maybe Evora or Coimbra. Though honestly, well, its presonal, but I think only Lisbon can keep someone occupied for months in a row.

Thank you all for the opinions, information, and suggestions. You have given me a lot to go on, for research and planning (my favorite part of just about anything). I was about to ask if anyone has ideas for how to stay in Europe for a year with two 3-month stays in Ireland (winter, including Christmas, and summer) and the 3 months in Portugal, but who knows what various visa/border rules will look like when I finally go! Or what border changes there may be! So, I'll wait on that one.
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