Try Sarbar's website
for lots of ideas on dehydrating your food.
Overdrying is mainly a problem with a few things like dried fruit which you want to eat in its dried state. You therefore want them dried to chewy consistency, not hard. For most items you want all the moisture out. Of course significantly overdrying your food will destroy some of the nutrients.
Experiment by drying just a small amount of each dish at first and rehydrate it for taste testing at home. The one time I didn't do that, I ended up cooking a chicken casserole with peas until the rest of the casserole was mush, but the peas were still the consistency of buckshot. Corn may have the same problem. Most other veggies, if cut in very small pieces, will dehyrdate OK, but I generally buy the freeze-dried "Just Tomatoes" dried veggies and add them after the rest of the meal has been dehydrated.