You need a license and insurance to apply any kind of herbicide. Keep in mind that dry weed and feed products are only about half as effective as liquid products. Naturally you would apply crabgrass control first. Fert is too expensive.
You work cheap. I don't see any way to cover your overhead. You need a charge for each sq ft so that at the end of the year your overhead is covered. And you need a machine and fuel charge for your truck and spreader costs, so that when they are worn out...you can replace them. And you need a penny or two for profit--otherwise why are you doing it?