4-6 cadets per mentor is about average. The tables are fixed at 10 seats. The answer is usually creative seating spreading over multiple tables. Tables are not pre-assigned. You just wander in and lay squatters rights to what you need.
Clothing is generally a dress casual for the day time events.
Your cadet will be wearing the gray tunic over gray pants. Be comfortable and dress in layers so that you can take off the sweater or jacket when you're inside. Slacks are accepted in all restaurants . It is a college campus but more than that it is a military post and the cadets work as well as study here. It could even be considered business attire.