Start with a business plan. Determine your costs and your break-even point. Things you need to consider:
Rent- you'll probably need to sign a lease. Can you afford that?
Utilities- may be included, maybe not.
Advertising- you need to find students, what's your approach going to be?
Equipment- big start up cost, especially since you are going to need lots of mats.
Fees- what are going to charge and how many students do you then need to cover your expenses? Are you teaching full time or part time?
Competition- are there other schools nearby or are you the only game in town? Most people won't travel more then 3 miles to train (read that in a MA marketing book once, don't know that it's true 'cause I have on several occasions).
Merchandise- are you going to sell stuff? If so, you will probably need some kind of vendors license.
hope that helps and good luck