PSF Types:
1. Villages - These are unfortified townships, the most common of all the 'minor settlements'. On their own they make a bit of money through taxes to the crown, but when a 'tax collector' (general/merchant?) is moved into the town the funds increase due to the villages not being able to skimp of their payments. Where the region capital is a fortress, the minor settlements are most likely to be of this type, villages providing for the lord in his citadel, when the region capital is a city however, the number of villages in the region is smaller (due to population movement to cities).
2. Castles - These are heavily fortified, and second most common of the minor settlements. They only make money when the castle is owned by a lord, but it is not much in comparison to villages. Generals can be granted hereditary titles of castles, becoming lords of the surrounding land and its profits. Young men (family members) can be sent to train here and troops can be barracked here for free on the kings behest. These minor settlements are quite common when the region capital is a city, but less common when it is a fortress.
3. Monasteries - These minor settlements are self sufficient religious buildings that are only found in certain areas on the map (catholic diocese') and are subject to the will of the Pope. They give no money to the crown but provide training for the nations clergy and give happiness bonus' to the region. However, if you convert your religion (late era Protestantism etc) than the loyal Catholics here will start to stir up discontent in your regions, unless you pass the 'church act' (a sort of building script maybe? Trying to simulate what Henry VIII did in England, confiscating church lands and their funds to going to the crown etc) which will convert the monasteries to your cause and start producing money for the crown.
4. Fortified Ports - (don't know if they will work yet, still checking it out) These are large mercantile and military ports that are found around Europe, and due to their strategic importance, they are adequately fortified by the sovereign (Im thinking places like Portsmouth, Marseilles, Calais etc) They produce tax for the king from the collectors at the docks, as well as the usual income that the merchants bring in. The importance of this minor settlement is huge however*, especially in regions that rely on their sea imports and exports; for if an enemy were to capture and hold the port, then the region would not gain income from it until it was retaken.
*My idea was to place the normal fort building on top of the port, so that you can 'capture' the port, stealing the enemies income.