Guest List size: Clearly this is an important factor. It is important to have a general sense of the amount of people who may be attending.
Personal style: Elegant? Informal? Someplace in between? Know what “feels” you want the venue to assist in creating. Some folks want a country club with high end catering and valet parking, and some want a camp with family cabins, the dining hall, and a fire-pit for smores.
Accessibility and Transport: Will your guests need special accessibility or accommodations while onsite? A coach service is convenient for out-of-town visitors. Many families choose hotels or resorts (and sometimes even a cruise!) specifically for the one-stop convenience.
Ceremony logistics: Beyond the guests’ needs, consider the ceremony needs for items like chairs, tables, microphones, projector and screens, etc. Make sure to confirm what is available from the venue.
Support: Any decently sized crowd of middle schooler students needs appropriate supervision. Some congregations event require that “proctors” are provided in proportion to the guests, much like for middle school field trips. Consider the value of dedicated supervision for the if there will be a significant number of adolescent guests in attendance. You don’t want to be the family billed for the plumbing damage in the venue’s men’s restroom because some younger guests thought it might be funny to flush full rolls of toilet paper. Trust me; I’ve seen it, and it’s not a pretty sight.
Celebration: Is your student more into passion projects and experiences than parties? Is a kid’s ropes course event, laser tag, or making simple tools at a smith something that speaks to your student? Open up the options of what the celebration might be. There’s nothing wrong with the traditional “party”, but there’s so much more “right” about celebrating the passions and interests of your student along with the accomplishments of the day.