This is a 9 hour event and needs to be viewed for food purposes as a group of events;
snacks 3- 5/6
dinner 5/6- 7/8
cake about 7-9
party/dance about 9-12
Each stretch of time would have a different array of foods.
Also, are you doing the set up, serving and clean up, and how much help do you have? Are you staffing the grill? The grill alone will take 2 full people for the main time of the party.
What you also need to tell me is whether this is expected to be a "come and go" or whether most of the guests will stay for 5-6 hours. If it is come and go, most people will stay about 2 hours. The usual split on timing if it is not come and go, is families with kids come from about 3-9. Adult guests for 5/6 to midnight. This very much affects the amount of food.
Also, is alcohol being served, and if yes, what?
If it were me, I would have a dessert bar in addition to the cake for the folks who are not there at cake time.