You need to keep in mind that any emails received to the primary Gmail account will be viewable by your wife so don't go ordering any Christmas/Birthday presents for here online with that account (buy her an N7, then you can keep this one for yourself.
Any email accounts added to the email client by either you will be viewable by you both, obviously no a problem if you share an email account.
It's going to be harder to memory manage the device with two people using it, apps installed by you both and any downloads or media added will take up space which you'll need to manage so not as to fill the internal storage.
Browsers, remember if you view any websites you don't her to know able either view in an incognito tab or clear the history.
Settings & preferences, could the way you want to use the N7 differ from the wife?
That's all I can think of atm, I'll come back and add more as and when I think about it.