I've been playing it again since adding Rule Britannia. Notched up a fair few hours now, but still learning. Each DLC adds new features too, so there is a constant learning curve. There is a new expansion coming out soon too, which concentrates on India and trade company mechanics amongst other things.
The AI does run out of money and it does run out of men, just like a human player. You just might not notice it. There are various ways the AI can collect both however, using the same things the player can. For example, if you have the DLC, you can use your estates to good effect. Some offer extra manpower; some offer extra money, at a cost of course. So when you run out of men, which happens quite a lot as a smaller player, you need to rely on mercs, or collect from your estates, or both. It might seem like the AI is constantly at war - sometimes they get dragged in to wars via alliances. Don't forget, the AI may join the war but if it is running low on manpower it may not necessarily be active in the war. The idea groups help a lot with these things too. But its a slow burner - unless you are very good/lucky, you need to play the game slowly to reap the rewards.
