It's even easier than that. Each app and/or store has a separate signin. So, you sign into the iStores with your shared Apple ID on both devices. You sign into the iCloud, Messages, and FaceTime (in their settings) using the iCloud ID for each user.
Hold in mind that for one user the iCloud ID and Apple iTunes Store ID are probably going to be the same.
iTunes Match (if you use it) might complicate things, since it needs to use both your iCloud account and iTunes Store ID. I'm not sure, and have no way to test it.