Annoyingly my Apple Music payment comes out of my account about 10 days before my payday (normally skint by then 😂) I was just wondering if I add money to my apple ID, will it take it from there first?
Yes.
How iTunes Store purchases are billed - https://support.apple.com/HT201359 - When you make a purchase, content credits are used first, followed by Gift Certificate, iTunes Card, or Allowance Account credits. Your credit card or PayPal account is then charged for any remaining balance." You can't change the payment type order.
Yes.
See here for details regarding accepted payment methods: Join Apple Music on your iPhone, iPad, iPod touch, Mac, or PC - Apple Support
iTunes & Apple Music Gift Cards can be used to pay for the Apple Music subscription. It should happen automatically.
If your account has enough gift card credit redeemed onto it, it will use that before charging your credit/debit card associated with your Apple ID.
Can you pay for Apple Music with Apple ID funds?
