I would have everything set up before you get boarders in. I think you will attract more boarders and have more boarders stay if you're all ready to go, rather than just having a few things done.
I would see how many horses you would want to take care of. Would you be hiring help or will you be doing this by yourself. Once you know your limit, either build enough stalls for that, or have a few run in sheds that the horses can go into.
What type of fencing are you wanting to put up? Each type (wood, metal, electric) all have pros and cons. For looks, I like the wood, but I also like this PVC fence (you have electric run along the top board) and I think that looks really sharp.
If you don't want to build an arena, I would just suggest you have a designated area that people can ride in (Not everyone would want to ride on trails)
As for legal advice, I'm really not sure. I've seen numerous websites that have boarding contracts etc, but it all costs something.
Also, are you getting insurance for the place? If you are, make sure the boarders sign a release form.
Oh, another thing, I would start looking/asking around for feed/hay suppliers. And look into something to do with the manure (My Barn owner spreads the manure, others I know have it taken away)
I've never read this particular book, but I have several books from Cherry Hill and consider it all great advice. Starting and Running Your Own Horse Business by Mary Ashby McDonald
Good luck in your horse business!