In standard gestalt you don't get bab or hit die no. You do however use the best of the bab and HD of your classes. Given that You are gestalting wizard//expert you get the better hd(Expert) and the better bab(also expert), so your bab and HD doesn't change. If you had chosen to gestalt say Fighter you would use fighter bab/hd instead of your expert bab/hd for the first level.