Too much according to some people. If you have no idea about where I you're doing, I would suggest easy difficulty and Portugal (though Castille is more powerful, I find that they are eventually have to fight against someone in Europe) and pretty much play an isolationist campaign. Ally with Castille and don't get on their bad side. I find that this keeps me from any aggression from other European powers.

Get the National Bank idea first (More important on normal or higher difficulty) and then Colonisation National Ideas and concentrate on expanding in the Americas. You'll get the hang of it soon enough.

If you play an aggressive game, make sure you don't go over the Bad Boy limit. A minor thing which is not really mentioned but keep at least one to one ratio of infantry to cavalry or more in a mixed army. It gives you a combat advantage.

Also, if you keep a couple of cavalry stacks, you can try to get an army into a province that an enemy army is retreating into before them which results in them losing more troops or complete destruction if enemy morale is low enough.

tl;dr: Play Portugal. Keep on Castille's good side. Colonise. Profit!