Let's see, just got done with stump grinding 2 x siberian elm stumps (4-5' diameter + long surface roots) we had taken down ~6 months ago. With our Vermeer SC252, it was about 6 hours on the job, including the time to load up the excess grindings and haul them off. Fridays are our usual maintenance/stump grinding/estimating day -- a nice way to wind down the week and ease into the weekend. So with that fresh experience, I would just say to make sure the customer has the right expectations from the outset. They need to know the depth you are planning to grind, or find out what their goals & objectives are -- just to reseed grass, landscaping, etc. Do they want you to chase out all surface roots? It's always good to communicate ahead of time that it is standard industry practice to rake all the grindings into a pile on top of the cavity where the stump was, so that they will compact down and compost down to soil and avoid a hazardous hole or a settled depression if the grindings were removed. If they are planning on immediately bringing in topsoil and want the excess grindings removed, be sure to charge extra!
As for tools, we use only Ames and Razorback rakes and implements, since they have lifetime warranties. We carry an iron rake, digging fork, and a 10-tine pitchfork for pitching chips, as well as a scoop shovel, ax, hatchet, and blower.
Also, carry a business card for someone else with a bigger grinder or tow behind unit. Don't be afraid to sub it out or pass it on to another stump grinding outfit if it looks unprofitable!