That's pretty common for the industry; our normal pattern is 5 12-hour shifts, plus 3 nights on call per week, with split days off. Times are bad at the moment, so we're on reduced hours of 10 hour shifts.
I don't pay the bills, but insurance for the vehicle isn't going to be cheap, plus you'll need accidental damage cover if you're going to work for dealers and body shops. If working in the LEZ, you'll need a compliant vehicle. A Transit or Sprinter with ramps(they don't have the weight capacity for a slidebed) is going to seriously limit the size and weight of cars you can legally pickup. The Transit we used to have couldn't legally carry an Omega, and they're not that heavy.
Ramps make loading and unloading cars with damaged suspension much more difficult. Did you do any winching of non-rolling cars? It's difficult to explain without actually doing, as some of the techniques are counter-intuitive.
My '60plate Canter does 300 miles on £100 of fuel. That's a sensible day's work.
Many(most? all?) of the cheaper trucks are priced like that because they're knackered; the Isuzu I had last sold for £5k with 540,000 miles on it but it was only LEZ compliant for another12months, and it still needed a a fair amount of work(which was why we sold it!) on both the truck and the body. And that was a well maintained one, but when a replacement alternator is £400, brake pads are £120, tyres £80 each(and it has 6) just the basic running costs soon mount up. At that sort of age/usage, hydraulic and electrical issues are also common.
So unless you're a really good saleswoman, with a healthy amount of cash to buy some decent kit, I think you're unlikely to make any money.