Here's City of San Jose City Hall exhibit policy: https://www.sanjoseca.gov/DocumentCenter/View/28147 written by Barbara Goldstein.

Having an appointed committee was extremely useful. It included City staff and outside persons. All proposed artwork was reviewed prior to installation so the potential for censorship of the show once installed was significantly reduced. If you were to do similar, having a jurist on your selection committee and a widespread approval/adoption of your goals, policies and procedures could hopefully reduce the power of a single judge to serve as the arbiter of the court values.

lots of interesting case law on religion & public forum...I'll leave that to the experts.

Good luck,