The "not good idea" part is if your customers require really cool A/C and warm heat during lessons. That would kill the battery, and cut your range in half... Just a thought.
Not true. No Leaf uses that much power for A/C, and the heatpump equipped models only use that much when temps are below 25F or so. The 2011 and 2012 Leafs do have power-sucking heaters, though. The S models lack the heatpump, but have effective resistance heaters (unless it's broken). I'd avoid the S, though, because like the early Leafs the heat still uses lots of power even for defrosting.