Maybe overwhelmed? Just wanna chat

Getting discharged from the hospital today with our 8lb, 36 weeker! I’m pumping about 6mL of colostrum every 3 hours but they have also been feeding him donor milk (37mL each feed) after those 6mL while we’ve been at the hospital. I’m wanting to supplement with formula until my true milk comes in. Anyone have experience with that? How many mL are you feeding of formula after feeding the colostrum? I don’t wanna do anything wrong and this is the only part so far that’s stressing me out