A Group Ceremony For Renewing Vows

I work for a municipality that would like to celebrate the remodel of a park with a stage. My staff and I are exploring the idea of inviting couples from the community to renew their vows...hopefully as a free service. I already have the park, minister, tables, chairs and PA system for free. What suggestions do you have to make this event extra special for the couples involved that wouldn`t be expensive (preferably free)? Would requesting the couples bring a pot luck item or a picnic lunch for thier family be perceived as tacky?