I think that this is an amazing idea.
I live near james so im also 20 -miles-ish away and would happily use your place (if good) at every opportunity i get!
I think that you could charge about £5-£10 a day!
Just remember to include things for all levels of riders.
Lastly, I hope this goes well for you, as i have been wanting to go barrow farm, but thats hours awway and cant get there.
Tom