This is a really good question.
It all depends on how you and your wife wish to progress. If you use your Apple ID, then Apple considers that new iPhone to belong to you as well as any other Apple products you may own - eg your own phone, is it also an iPhone?
If, on the other hand, you create an Apple ID for your wife, then Apple recognises her ownership of that iPhone.
In case 1: apart from having her own phone number, her iPhone and yours will effectively in sync. You can, of course, select exactly which features on her phone she wishes to sync with yours via iCloud. Contacts? Calendar? Keychain? Photos? Reminders? Notes? Safari with all its settings and Passwords? And so on.
Messages requires careful consideration because unless you undertake certain adjustments (which I could outline), you will both receive each other's messages. Many husbands/wives are happy with this. Quite a lot aren't.
In case 2: You and your wife have your own phone with no crossover or sync between them. You and she can separately sync whatever you both want to another Apple device which you or she own. But you cannot sync anything between your selves.
However, say you - can Share Contacts, Calendars, Photos etc with your wife. They remain yours, but she sees them and can make adjustments to them as part of the sharing process.
With all that out of the way: which is it to be? Your Apple ID and you own both - or you and she are completely separate individuals??
Ian