There are many factors that influence the portioning – time of day, plate size, how long service is, etc., but I would estimate the food in the following way:
7-10 portions salad per head of romaine – cut one, portion it out then multiply
30 portions per litre of dressing
6-10 portions pasta salad per litre
40g total meat and cheese per person
50g cooked turkey per guest
10l cranberry sauce
1 lettuce rollup and 1 cupcake per person – depending upon the size
5 large platters of sliced fruits and berries
20l of hummus
If you are in doubt, put together a small version of this menu, plate it, and it will be easier to visualize and adjustments can be made accordingly.