Ok, you were right. I found out that unrest spreads from three sources. AI causing unrest, the normal growth (seems to work as far as I can tell) and battles / sieges. Seems to be really well done; I just didn't get it at first.
The more I understand of the unrest mechanics the more genious I think it is! This even cancels out my last original point because if you don't pay properly attention on your cash flow and unrest there may be really game changing surprises in there when you think you've already won. It's all logical once you find out how.
Ok, point two still stands. The one about having an overview of the troops in a province. And selecting them.
Point three, I don't know yet really. I noticed that troops that are not 'at home' get the status 'waiting' and a time how long they are in that waiting state, so you got kind of control or at least early notice. I'm still trying to work out the point though.