As of right now, I'm feeding mine a mix of 5 parts oatmeal, 2 parts corn meal, 1 part flour, along with a small ammount of dried, ground calcium and vitamin fortified mulberry leaves (optional/experimental). If you're going to go into raising a lot of mealworms, bran is what I've always heard recommended.
To drink, they always have available slices of potato, banana peels, and the occasional slice of orange which is changed appx every 48 hours.
I don't have any exact lifespan of the beetles, but I know that some have lived as long as four months before dying, some only lived half that.