2 iPhones: 1 Apple !D, or 2?

I have very little experience with iThings.
I have a Tracfone iPhone SE (working towards an eventual unlock), and it's set up on an Apple ID.
I've got a 2nd iPhone SE (also Tracfone locked, for now) that I need to activate.

Can I, and should I, set up iPhone #2 on the same Apple ID, or start another Apple ID? Any advantage or disadvantage to pick one route or the other? (Assuming both routes are possible....)

FWIW, after I get it unlocked, the second iPhone may eventually get used by my SO as a backup phone and/or iPod, She has an older iPhone she uses for listening to music and podcasts, but I'd prefer to manage the new one myself until I get it unlocked.

If the phones are being used by different persons (e.g. you and your SO), I recommend using a different Apple ID for each phone. Otherwise, iMessages intended for one of you or the other might wind up being sent to both. You'll both also have 5GB of free iCloud storage each, as opposed to having to share 5GB on one account.