if you let anyone ride your horse or pony and give them a lesson you also need to register as a riding school (see a recent edition of nag and dog or search the website)
financially - big answer - don't do it !!!!!!
insurance will be the least of your problems.........and if you are going to be paying rent for the site and charging on top of that you'll be working d**n hard to cover the rent, insurance, business rates, etc before you even earn yourself a living
most 'successful' livery yards are owned, not rented, as the rent just kills all the margins stone dead these days
also - under the newly signed animal welfare bill you will have to be licensed by the local authority and be inspected by a council official and also a vet !!!
Well I am going to save up to buy my own place, then gradually build around 10 stables as I earn enough money. I also want to take horses in for schooling and also be a freelance instructor to get a bit more lowie.
Once it is up and running though it would be nice to just sit on my ass all day and earn £20 per week times ten