This is a hard nut to crack.
You'll be up against people charging as little as £7 per hour so will need to show that you are worth the extra. This is known as the chicken and the egg!
You charge what you can but why bother for £1 per hour per person Gross Profit, unless you have lots of staff out there!! If you are above board and employing then even if paying minimum wage you'll be looking at approx £6.85 per hour costs. This is on staff alone.
Best of luck.
p.s. your insurance should already cover you but the best thing to do is speak to your broker to confirm. Treatment risk is worth adding on if not already included; check your policy as it may well be there.
p.p.s. on the plus side you already have the ear of a decent customer base, there's your starting point......