Apple ID for child younger than 13 and parent with no Apple device
You will have the least headaches to bribe (or make time) to wipe the device - and set yourself up as the Family Owner using your own Apple ID.

To start, just use parental controls and have the child come to you for authorization. Once you have gotten a few purchases in, maybe with a $25 gift card - then consider if you can approve purchases from an inexpensive used iPad with your credentials or via email from your device of choice and then put your child’s account in as a managed / family / child account.

You can set up your family at https://appleid.apple.com once you register yourself first on the device. Put in your charge card, address, and save your security questions - make sure your cellular and recovery email are safe and operational if you go two factor auth.

You asked about 5 great questions in the original post, so hopefully this is enough to get you started. Take the time to set up your account, then make a family and create the child accounts. You will be super glad you spent the time to use the managed route.