The inconvenient thing for you , in terms of the food planning, is that with a 6PM wedding, most people will not eat before coming so even though you plan an informal menu, it has to be enough food for it to be dinner. Thus, your menu, while good choices, is light.
For example, you need 50 pounds of meat, 4 ounces of meat plus 2 ounces of cheese per person at a minimum, I would double the roast beef and do 1 1/2 times the amount of each of the other meats, then do at least 22-25 pounds of cheese.
You need to use the condiment table on the sandwich page to do the condiments for the sandwiches. Veggie tray is OK, you need to check the dip- see the veggie tray page.
I would definitely add fruit trays, pretty, popular and can be done ahead. Or at least make sure that you have plenty of fruits with the chocolate fountain- and do read my article on them, please, for safety's sake.
The 4 gallons krab slad is OK, people will use it as a sandwich filling, but you need at least 6 gallons of potato salad per 100= 12 gallons, to give a small 1/2 cup serving per person. I would add a pasta salad of some kind, at least 6-8 pounds dry pasta, or chips with salsa and nacho cheese.
Hope this helps.