I'm currently finishing up a game of that myself. It's not horrible, but the time constraints is a bit of a nuisance. My profit dropped a bit at the start after losing the trade and having to drop my taxes to low for happiness, but I managed to recover it (11k -> 3k -> 17k). I was a bit irritated to find out that making a new vassal afterwards still won't let you keep it.
As far as armies attacking weak points, I've been careful to expand in ways that don't leave a lot of them, and most of my territority can be quickly reinforced via railroad.