cold bar:
lettuce
tomato
onion
sour cream
picante sauce
cheese

dessert:
a fruit tray:
watermelon
honeydew
grapes
pineapples
strawberry
kiwi
cherry
bananas
wedding and grooms cake

drinks:
tea
sherbert punch
bottled water
reg. fruit punch

May I suggest you tweak this a little? You need an appetizer area, and here is info from an upcoming article on why:

Before the Buffet; Why You May Need an Appetizer Table
A self-catered buffet is a real challenge to the organizers, and things don't always come together as smoothly as hoped. By planning and setting up an appetizer area or "nibble table" which is ready when the guests begin to arrive, the cooks and servers have time to complete the arrangement of the dinner buffet. This is especially critical if there are children among the guests, or there is a wait before dinner, as at a wedding reception.

This does not have to be complicated. Three items, plus a punch, or two if one is alcoholic, are sufficient. Typically, including a fruit tray, a cheese tray and an attractive dip or spread; or you can go with a dinner theme such as TexMex with chips, salsas, Texas caviar or corn dip and guacamole, maybe tiny shooters of Mexican seafood cocktail if budget permits. 1/4 cup each dip and 1 pound chips or bread per 10-12. This off-site link might give you some ideas:
www.rd.com/slideshows/10-perfect-mexican-appetizer-recipes/#slideshow=slide5

One appetizer service area is needed for each 100 guests.

Now, about the buffet itself.

enchilada casserole; two per person, I would make 1/3 cheese only as most of your other food is meaty
rice- 8 pounds dry per 100
pinto and refried beans, consider making vegetarian style (no lard); about 20 pounds total dry, divide according to local taste

Nacho bar
taco bar
chicken,beef fajitas
Combine these. Put out soft tortillas and taco shells as discussed on the taco page, and another 1 pound chips per 12 at the start of the table.
Beans
Taco meats
cold stuff
fajitas
Amount of meats? About 2-3 ounces taco style, 3 ounces beef fajita, and 2 ounces chicken fajita per person
2 #10 cans nacho cheese sauce per 100, plus 1 extra unopened can in case you need it.

cold bar, I would put this in front of the meats, after the enchiladas and rice,and between the tortillas and the meats, it cuts down on the amount of meat taken. Use the taco bar article for amounts.
lettuce
tomato
onion
sour cream
picante sauce
cheese
Ranch dressing- several quarts- people make taco salads

dessert:
a fruit tray:
watermelon
honeydew
grapes
pineapples
strawberry
kiwi
cherry
bananas- be sure these are dipped in citrus juice as soon as peeled and cut, or they will turn brown. Other choice- roll in mayo and crushed peanuts

wedding and grooms cake, OK yay chocolate

tea- 20 gallons, 1/3 unsweetened
sherbert punch, 10 gallons
bottled water- 1 per person
reg. fruit punch- how about an aqua fresca in keeping with your theme? melon or watermelon or hibiscus/Jamaica?- 10 gallons

I would add dinner level coffee from the beverage page- everyone likes it with cake.