Hey Tpweste,
Those are some great questions! We see that you checked out the article about backup methods. First, here's an article that goes over what iCloud backs up: What does iCloud back up?
Now that you've gone over all the information of what iCloud backs up, we need to check what backup was enabled on your device through iCloud. To check this, go to Settings > Your name on top > iCloud. From there, check to see what apps are enabled for iCloud. If you see Contacts and Messages enabled for example, then those are backed up on your iCloud. Turning them off will stop the backup but remain on your device. However, you'll need to enable iCloud again in order to have them backed up.
To create your own Apple ID account, follow the steps from this article: How to create a new Apple ID
Using your own Apple ID account can help you access all your downloads and purchases that you made through your account. If you have purchases from your mom's Apple ID, then those purchases are tied to your mom's Apple ID account and therefore, you will no longer have access to them on your own account. You'll need to download or purchase your own apps, subscriptions, etc. using your own Apple ID account. However, you may have access to some contents through Family Sharing and all that information can be found here: Set up Family Sharing
We hope the information that we provided was informative and helpful.
Cheers!