What amount to you think? How strong is the dry mustard?
I'd start off with at least 2 teaspons and work from there. It's not as strong as you may think. I use it in homemade hotdogs or brisket rub. For beans, I usually throw in some brown sugar, bacon, maple syrup, either ketchup or tomatoes, maybe some diced ham, onion and uh the beans..