K.S.
As far as quantity the general rule for a tossed salad is about one cup per person. With all that other food I certainly wouldn't plan for much more than that. In our family we have always done individual salads that were placed on salad plates before people sat down. My favorite (though a bit labor intensive when I would make it for 20) is as follows.
Ingredients:
Mixed salad greens (torn in bite size pieces...I used to buy Byerly's mix that you bag yourself)
Ruby red grapefruit (peel and then peel the "skin" off each section...this is the time consuming part but the results are worth it)
Pomegranate seeds (peeling the pomegranate does take a little time too)
Honey
On each plate place a scoop of lettuce and three grapefruit wedges. Sprinkle on pomegranate seeds and drizzle with honey.
One note, if there are tons of younger kids it is best to substitute oranges on their plates instead of grapefruit.