AFAIK: You will need both a DOT registration and a Motor Carrier registration since you will be hauling freight in interstate commerce. You will need liability insurance appropriate to the freight business, as well as physical damage insurance and contents insurance. As a sole proprietor, you probably will not need workers comp. If there is any chance a customer will EVER step foot onto your trailer, you will need liability insurance for that also.
You may also need a commercial drivers license.