The difference between start-up and operating costs:
Start-up costs: are the expenses necessary for setting up the business, before the business can open to the doors to the public.
Operating costs: include the costs to keep the business running.
Monthly operating expenses are the operating costs, the money that ensures the business runs smoothly and lets us see how much we are spending every month.
again here is a link with some guidelines to help us visualize all the monthly expenses: