Find old ITunes account

You can use any email address to create a new Apple ID. It can be a hotmail address.

click here ➜ How to create a new Apple ID - Apple Support

and here ➜ If you forgot your Apple ID - Apple Support

As to your music, unless it was purchased from iTunes, you won't be able to access it even if you do figure out what Apple ID you were using on the iPad Mini, or you were subscribed to the Apple music subscription service and it got uploaded from a computer at some point.

For music synced from a computer, you would need to sync it again form that computer onto the iPhone.

click here ➜ Use iTunes to sync your iPhone, iPad, or iPod with your computer - Apple Support

Also, you should make sure if this is a second hand iPhone that their Apple Id has been entirely removed from the iPhone, and it has been completely erased. You should set it p from scratch as if it were just taken out of the box for the first time.

click here ➜ What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support

On an iPhone, go to Settings ➜ Apple ID ➜ Media & Purchases ➜ Sign Out, and sign in with the old Apple ID and its password.

Do note, that any downloads through the old account, will lock the current account out of the iPhone for 90 days.

If you are trying to accomplish something else, then please clarify.