Metaluna

I don't know what Campy recommends specifically, but as a general rule I shoot for around 3,000-5,000 miles for any loose ball hubs from any manufacturer. I'm not very good at tracking mileage though, so I generally just do them once a year if it's a wheelset I ride often. If you ride a lot in wet or dirty conditions, you probably want to do them more often (though the Campy hubs I've used are pretty well sealed).

As for level of difficulty, if your wheels have Record-style bearing adjustment, they are about as easy as a non-cartridge hub can be (no cone wrenches needed). But I still wouldn't call it simple if you've never serviced a loose-ball hub before.