Diagon Alley is in one park, and Hogsmeade is in the other, and the Hogwart's Express ride goes between the two, so you'll need a park-hopper to ride that.

If all you're doing is the Harry Potter stuff, you probably won't need multiple days; we ended up seeing both sections in one day.

I would buy one of the interactive wands, and see if you can make the gizmos in the windows work. My kids loved that, your wife might, too.

Enjoy. It was a blast for us.