To your first question, yes, you can save a game and then load it later to continue playing. It's pretty much like any other mod in that regard.
To your second question, raiding villages can be good or bad depending on how and when you do it, and who you raid. Generally speaking, raiding in the first month is mostly a wasted effort. None of the other settlements has resources yet, for the most part, and the world population is very low (except in Custow). Later on, though, it's a ton of fun. I raid bandit-held settlements in the second month onwards, and I plan on raiding the peasant-owned settlements after my first settlement becomes fully upgraded (e2m2).
As for getting more peasants to join your settlement, there should be a ton of traveling peasants on the world map, especially around Custow. That's not the only way to get new peasants, either. For every +2 in relations you get with Custow you can talk to the elder peasant (wearing a black robe in the center of Custow) and ask him to send peasants to your settlement. Also, if you ride to your settlement and stay there for a while some peasants should just randomly wander in. When they stop walking you can talk to them and ask if they would join your settlement. They might refuse, but usually they'll be happy to join.