If you delete your main nothing happens other than losing your save files for games. I would keep it though on your HDD cause theres no need to delete. Some Xboxs let you get a free month on new accounts 2-3 times but I though they stopped doing it. There is an option somewhere in the profile setting for the account called Auto Sign In or something. Enable that on the account you want it to automatically log in when you start the XBox.
