Sharing an Apple ID on different iPads, but having different Contacts
Perfectly possible, you essentially both need a free iCloud account, that you log into for the purposes or mail/calendars/notes/contacts etc etc.

You each log into iCloud from within Settings &gt; iCloud with your unique ID, and turn on any appropriate option within that page once you are signed in.

Then, for the App Store, go to Settings &gt; iTunes and App Store and log in again, only this time simply both use the the same ID that is associated with all your past purchases.

You can log into different ID's for different services like Facetime/Messages/App Store/Mail at the same time, it really doesn't mind.