Transferring to new Apple ID?

Hello! I have had an Apple phone since around 2012. When we set it up, we put my phone number/information under my dad’s Apple ID for safety purposes.

Now, 12 years later, we are running into some obvious issues with this tactic. He receives all of my text messages on his iPad, which also contains some games he would like to save his progress on. However, his phone is linked to a completely separate Apple ID - the only devices that share this one are his iPad, my phone, and my iPad. So my phone number etc are all connected to his account.

I don’t care about losing Game Center progress, but I would like to keep my photos and contacts, if possible.

Currently, the approach I am considering is this:

1. download photos to a computer
2. unlink my phone number from the original account
3. log out of his Apple ID and into my own personal ID

I know we could also swap his iPad to his actual ID, but I don’t want him to have to lose any Game Center data that’s important to him.

Would this work? I’m not sure what all I am going to lose when I switch over, and what I need to prep for (i.e. writing down all my contacts). I also know that swapping Apple IDs isn’t really what Apple wants its users to do, so I’m not sure if anyone else has experienced this or if there’s a better approach!!