Eliminating separate user after migration

See Transferring files from one User Account to another. The account you migrated has all your data. Why not log into and use that account? This will save you the work to transfer all your data into the new account. Then just delete the new account and stick with your migrated account.

Sure. Just pay a separate fee. Seriously, if you wish, you may keep the new user account for a "test" account. To delete the account, you need to be logged into the migrated account you want to keep. Open Users & Groups preferences pane. Click on the lock icon and enter your admin password as requested. Select the user account you wish to delete from the list, then click on the Delete [-] button. You will be given three or four options from which to choose. Choose the last option which fully deletes the account and click on the OK/Delete button.

Here you go, please click Delete a user or group on Mac

You shouldn't lose anything from the account you migrated, if you migrated everything allowed. You will have the same user account on the new computer that was on the old computer. Of course, this will include third-party applications that may need upgrading if the new computer's version of macOS is a later version than what was installed on the old computer.

The Dock items are only an alias so right click the ? in the Dock and select Options - Remove from Dock.

Yes, that is what I'd do, in fact I always keep a spare admin account for emergency Purposes..