Good ventilation does NOT 'go without saying' - it's important.
OSHA and EPA compliance will be your biggest concerns. Do not trust a general construction company to know how to properly build a range. You'll need someone who's done it before.
Have a good attorney look at your customer liability waivers to make sure they're absolutely airtight. Expect one suicide every two years on average, and no matter how well you watch things, negligent discharges will happen. It would be a good idea to put all your employees through the NRA RSO program and first-aid training.