Apple Music Asking for Payment on New iPhone – 3-Month Free Trial Not Available

You should expect the battery to drain and the device to be warm for about 5 days after set up. The OS is indexing your files and analyzing your photos for object detection. The exact time it takes depends on how many photos it has to analyze.

After that you would need to check the apps you have installed consuming the battery at Settings > Battery. The ones that show background processes are using your battery even when you are not using the app.

Since you said your Apple Music subscription is not "currently" active, that implies it was active before. That would exclude you from the free trial promotion with device purchase. If you shared your Apple Account with someone else, they may have also used a trial that would exclude you. All the information about the free trial offer is available here

https://offers.applemusic.apple/new-device-offer

You can always contact Apple directly and they may be able to tell you when that Apple Account was used previously for an Apple Music free trial. Any subscription your previously had with Apple Music would have started with a Free Trial.

Contact Apple Support - Apple Support

The offer is for new subscribers only. As you previously subscribed, you are ineligible.