Cannot obviously be totally certain, but there is a release I believe of iOS 18.1 beta for the 16 devices.Will installing this result in potential issues tomorrow with the new phones and porting things over to it?
If you're going to restore a backup as you are already running 18.1, then you'll need to install the beta on your new phone prior to restoring. Likely means setting up as new first, installing the beta, then erase all contents and settings. Set up again. Restore.