What to include for a buffet ?

That's a lot to cater for. Maybe a couple of quiches that you make the day before or stuff that you can freeze beforehand to make the load easier.

Not terribly imaginative, but a lot of people love the thought of hot-bars, such as pasta dishes as Marga mentioned, baked potato bar with lots of different toppings, taco bar with all the fixings, and nacho stuff, people love tacos. A big pot of crock-pot soup, or even two choices, goes a long way to feed a lot of people, too. Maybe some bowls of salads like pasta salad, a chicken salad, bean salad, cole slaw, or whatever--all with the fixings already in them, so you don't have to mess with adding bottles and jars of whatever. I would make the dessert a hand-held one as well---homemade cookies, cupcakes, and such. I am sure whatever you fix, will be delicious.

I once went to a very nice and easy buffet sort of dinner. They had cooked several kinds of pasta and they had several sorts of sauces (from Alfredo to bolognesa, from pesto to seafood). Each of us served whatever we wanted. There are several sauces that are tomato based some of them that are even eaten by vegan people. That can be the main dish and pasta can even include ravioli and other filled pasta. And to begin with you can have antipasto.