15# ground beef-18-20
12# shredded chicken-15
10# can black beans (for vegetarians)-OK
200 each hard & soft - OK
10# chips- OK
3# shredded cheese- 5-6
2 10# cans nacho cheese-OK
6# shredded lettuce- go 7 or 8, just don't open the last bag till you see how it is going- some people will do salads
8# tomatoes-OK
10# can black olives-OK, prob some left, sliced
2 gallon salsa-plenty, consider having a mild and a hotter
1 gallon sour cream-OK
1 gallon guacamole- will prob run out, I do 20 pounds/ 10 quarts
1 gallon jalapenos-OK
8# dry rice (for Spanish rice)-OK
2 10# cans refried beans-OK, get vegetarian (no lard) and mark the serving container

Suggest you add a few bottles of shake-on hot sauce and 6-8 bottles of salad dressings. Consider also several bottles or a #10 of plain taco sauce

Stock no more than will be eaten in 1 hour, MAX. Replenish potato bar as needed.
Toppings which have been at room temperature CANNOT be returned to the refrigerator and must be discarded.
Do not add fresh toppings to old toppings; let the dish be emptied and replace the entire serving container.

As for the setup, you are right about effect. The jalapenos, olives, black or refried beans are all eagerly sought by nacho builders , so put near the chips, and many will also add some meat. Consider having the meat serving spoons and some others be the type used for salad bar toppings, they control portion sizes:

www.homedepot.com/p/Carlisle-Polycarbonate-Black-Buffet-Spoons-Set-of-12-447003/204658501