The answer to your questions depends on what type of job you hold, and whether your employer requires you to notify it of any arrest and/or conviction or court disposition. Ordinarily an employee handbook would remind you of your obligations, or upon hiring, you may have signed a document that requires you to provide this information. Without knowing more it is difficult to answer your question. Moreover, most licensed professions require you to notify the licensing entity upon arrest, and certainly disposition of a criminal case. Assuming you do not violate any other laws, satisfy the conditions of your supervision, including payment of fines, fees, and costs, and complete your community service, you would qualify for an expungement of this case as your attorney advised.
If you were given a 1 year supervision sentence, you will have to wait 5 years (6 years total from date of plea) to file a petition to expunge. The 7 year number is incorrect.
The expungement will cover the listing of the arrest on your record. Supervision is NOT a conviction. The State can keep the history of your arrest until you file that petition.
The five year wait is for expungement and exists because a second charge of retail theft in five years can sometimes be made a felony.
After three years (from the finish of your supervision you can move to seal the arrest records. This allows the government to see them but takes them out of public view.