I planned one of these about 5 years ago, and here's what I did. I wanted to keep it simple because I knew I didn't want to be the hostess stuck in the kitchen, obsessing about what could be going wrong. Enter the crockpot!
OP, if you don't like the slider idea, I suggest you have make-your-own tacos as your entree. Just get some ground beef and shredded chicken (I can tell you the easiest way to do this if you want), stick it in 2 crockpots, season with taco seasoning, and set out the bowls for the lettuce, tomato, shredded cheese, salsa. Kids of all ages love making their own. And veggies can just make meatless tacos.
If you do this, all you need to provide is some salads and dips. I'd forego coleslaw and potato salad completely (unless you want to make the potato salad from scratch). Maybe put together a tossed salad, some 3 bean salad, and something funky like carrot and raisin. Everything else could be dips or fruit/veggie platters.
And I also agree with PPs that you're not serving dinner to 70 people, so don't panic over quantities.