Do I need to fully charge my new iPhone 13 Pro before using it?

No, there is no requirement to charge for any specific amount of time. Although I would suggest charging it and leave it attached to the charge circuit during any iOS update, or data transfer process.

Do I always have to charge my iPhone 12 Pro Max to 100% every time?

IPProMax12 wrote:

Do I always have to charge my iPhone 12 Pro Max to 100% every time?

No, there no requirement to try and micromanage the charging process. Charge the phone at your convenience.

do i have to charge my new i pad