We are thinking along the same lines here. I am thinking of organizing it through local churches.
I would caution to get some legal advice, even to have a lawyer on site, which might be through a pro-gun organization, in case you get official harassment, trying to bluff and bluster you into shutting down.
Also to have several individuals designated to video at different angles if they get a signal. Getting a face shot of a provocateur really sucks a lot of wind out of their sails.