It is hard to pump & feed together la!! You can tighten the bra of the side of breast you are not using, then you can reduce the dripping problem la!
You don't really have to know how much the baby drink, you just have to make sure that the baby has about 6 to 8 wet diapers a day and the baby is happy and lively.
As I sometime pump and sometime feed my son directly when he is a little baby, I know that he normally drinks 2 to 3 oz each time; so 4 oz each time as told by the nurse is a quite a lot.
For the amount of milk you pump, the more frequent you pump, the milk you will get.
For freezing milk, I will suggest you to freeze 4 oz by 4 oz as it is better to defrost 4 oz by 4 oz as well (because defrost milk has to be consumed within 24 hours).
Hope you find this sharing useful!