1) You will find anything that you currently have on your account (files that is) in that backup and unless something has gone wrong when either the server creates the backup (which is a minimal risk that it happens) or when you extract the backup on your own computer, all current files should be there.
2) Easiest way to start over is to submit a ticket with the help desk and tell them you want to start over and ask them reprovision the account, ie set it to the state it was once when you signed up.