How do I stop all the sauce from being absorbed and the pasta going soggy?
The secrets to a good pasta bake are:


Pick the right pasta: unless you are making Lasagna, tube shaped pasta is the best choice because it holds sauce, and tends to be thicker. Thicker pasta is better than thin in a bake, because thin pasta will get soggy way too easily. Penne works fine, so does macaroni. I think rigatoni is best, because it has ridges on the outside which help hold sauce on.
Undercook the pasta: if you cook the pasta until it's done and then bake it with a sauce, it will keep right on cooking and get mushy. What you want do to is cook the pasta until it starts to soften, but isn't quite edible yet. A minute before you reach al dente would be how I describe it. This way it cooks perfectly as it bakes.
Right amount of liquid in the sauce: the ideal result is to have a bake that holds together well without being dry. The pasta will absorb water as it cooks, so you need enough liquid to allow it to rehydrate, but not so much the dish comes out runny. Once it's all mixed and in the baking dish, check to make sure there's some liquid on the bottom. You want enough loose liquid to cover the bottom. If there isn't enough add some of the pasta water or stock - slowly, don't overdo it - then bake it covered for the first 15-20 minutes. If there's too much liquid in the bottom, bake it uncovered so more evaporates.


As for what type of sauce to use and what to put on the top, it really depends on taste. Some people use a tomato sauce, others a white sauce (mac and cheese is a white sauce with cheese in it), some people use both, typically layered. You can do a meat sauce or vegetarian - chunky or smooth, there's too many possibilities to list and it's opinion based on what is best. You need to consider the audience and what their dietary needs/preferences are and choose a combination that satisfies as many as possible.