There are liability form on the net for boarding, riding, lessons and training. All you have to do is alter them to fit your needs.
If you are calling yourself a business then yes you need to get all legal beagle in that aspect.
As for price, this is my opinion and how I work things.
I charge for my gas, they want me to travel they pay it, if its more then a 1/2 hour away.
I train the owner and the horse, meaning I train and the owner I need to make sure knows how to handle the horse and use the methods I used to train his/her horse.
Price depends really, are you confident? Then make a confident price. Trainers around her get 65+ an hour.
The forms are always my priority and I get the owners signiture and I sign it under her, I make sure I have the training hours on the paper as well.
When I do work with the horse I keep a journal, got here such and such time, horse was quiet brushed the horse worked on ground manners etc. and login the time I left and how the horse was. This helps me keep track of progress and also shows the owner the progress.
Good luck!! And most of all Enjoy.
Live to ride and ride to live!