You are right, I misunderstood. I see now, you did your homework very well!
I am afraid I dont have too many tips or advise. Buying land in Portugal is quite easy, you just need a fiscal number, which you can obtain at the finanças office, it will cost just a few euros (I forgot, maybe 10 or 15 euros). A solicitor can help you for a reasonable fee, to do the legal work. They will ask the neigbours of the land you want to purchase, if they want to buy it, according to the local laws. Also, they will calculate the taxes and fees you have to pay. Since I bought only once a plot of land 3,5 years ago, I am not an expert on the topic. I made my purchase in cash (I am not a big fan of banks), but I think recently the law changed, so cash transactions above a few grand are illegal now (criminals use cash, so cash is criminal, or maybe its just to make us a bit more dependent on the very solid banking sector, lol).
I agree with you, the location, distance to a bigger town, is important. When I came here, I thought a bicycle would be enough, but I soon found its not that nice to cycle 15 km to the nearest town, to buy groceries. Me being used to the low countries, I found cycling in the hills here is especially in summer not always fun.
Another thing to consider is the climate. There are big differences locally. Personally I think I did a good job buying the plot in this area, since there is enough rainfall here, but not too much like further to the north. Temperatures are not too low in winter, and not too high in summer (this summer is colder than average so far, maximum temperatures averaging below 30 degrees) I am about 380 metre above sea level, in the winter it can get a few degrees below zero, but not too much, so lemon trees survive here. About every 100 metres higher, average temperatures drop by a degree celcius. If you want to live next to a stream, there is a big chance you will end up somewhere in the lowest part of a valley. In winter that means less sun hours, and more fog (some days you might not see the sun at all in the valley, with higher uphill sunny weather). Also, the water from the streams might be polluted, also the wells could be polluted by farming uphill. Many locals here love Monsanto products, they like bare ground around their grapes and olives, and pesticides are so convenient. My plot is almost in the top of a hill, so I think my water is pretty clean, since there is just some forest uphill. So if you want to live close to a stream, I would suggest to stay close to the Serra da Estrela, then you are not too low, the closer to the mountains, the cleaner the water will be.
Thats my advise I can think of, at the moment.