These back-office activities are part of the overhead of doing business. Someone has to open the mail, pay the bills, keep the books, remit taxes, provide customer service, handles collections, and do the hundreds of little things that make up running a business. It is a serious mistake to ignore the demands that these activities will place on you and your business. A good starting point is to make a list of all the activities that someone will have to perform to keep your business operating. A house painter has to do a lot of things that are not directly related to applying a fresh coat of paint to a house.
Someone has to purchase the ladders, tarps, paint and brushes, masking tape, and other necessities.
Someone also has to bid on jobs, bill customers when jobs are completed, and deal with complaints if a customer isn't happy. And those tarps need periodic washing or replacement. All these things take time. One way of managing the time spent on administration is to let people outside the business handle certain jobs for you. This can reduce the time spent on back office work, in exchange for a cash outlay.