RE: indoor range insurance
I asked the owner of the range I shoot at about this last night, and he suggested joining the NFAA if you want insurance. It will cost you $900 plus a certain amount based on how much you do in business every year. He also suggested that most of the liability for the range comes from renting equipment out, and that he doesn't rent equipment purely for that reason. Also make sure to put "Shoot at your own risk" type signs out and make sure you have a red warning light that is always turned on when it's clear to go downrange. You can also make everyone sign in (and sign a waiver) before they start shooting if you wish.