I'm in the same boat as you. I am working toward trying to open Pro this year. Over the years I have gathered a few books that i think have helped me get ready for this. One is the old standard from Phillip Morris called "How to operate a Financially Successful Haunted House" and the other is called "Field Of Screams" by Michael M. Cruz.
Other things I have learned from Leonard Pickel and others is stuff like:
-permits - things like certificate of occupancy and fire inspection
-Fire codes - I'm not in the city and the county says they don't have fire codes for rural building out here
-liability - as sole proprietor someone can sue and get your house, I'm going for LLC, Limited Liability Corp, they can only sue and get the asserts of the company
-Insurance - find a special events agent, the guys covering your house may not know how to help you. and if your leasing you may also have to get extra to cover him from being sued
-Advertisement/promotions - a lot of the stuff i have read says this is as important as the haunt itself.
some of these depend on the codes where you are running your haunt. if its in the city limits check with the city office. if your out of city limits check with your county office for what kind of codes they require.
Leonard has some great articles on his site on some of these things at: