I checked some of the founding fathers;
Paul Revere is the man who lets the colonists to take up arms.
Drake is the one who strengthens privateers.
John Paul Jones (or something like that) is the one who gives you a free frigate. (I don't think this guy is helpful later in the game, because you can use your liberty bells for something much more necessary.)
About the bug(!) i mentioned; normally a unit of soldiers needs 50 muskets. For example, when i have any number of muskets below 50, it can even be 1, any civilian in the colony takes arms when attacked and they seem as soldiers in the combat display. It could be made intentionally just to show the basic aspects of militiamen, people going to war with all they have, even if they don't have enough
But it has nothing to do with fortifications as much as I experienced so far.
And yes, population of a colony which has stockade can't be dropped below three nor it can't be abandoned.