The potatoes have spoiled. They were not brought up to temp fast enough. You can't use a steam table to reheat, it's to hold.Read your states guidelines, this should have been in your food handlers permit test.
Depends on what your market will bear. Most would charge a day rate, in Manhattan it will be much more than in a flyover state. I would say $200-500 a day depending on your location.
@Brandon ODell, a member here owns a personal chef business and is involved in this type of venture. Read some of his posts, I know this subject has been talked about in the past.