Migration

If you would have migrated from your TM backup during the setup, then your user docs, music, other media and preferences would have been properly transferred into the newer apps.

From this point you have three options.

1. Start over. Erase and reinstall macOS on the new Mac, then properly migrate from your Time Machine backup.
2. Migrate as is, which will give you a new and an old account, where you can painfully merge the old into the new.
3. Leave things as they are and then slowly move data from the old Mac to the new Mac using an external drive or over your local network.

The easiest, fastest and most reliable way to migrate to your new iMac? Is to plug the Time Machine backup drive from your old Mac into the new Mac and migrate from it during the initial setup.