Re: Going back to work
The rule of thumb is to leave around 1.5 oz per hour of separation. Some babies will take more than that, some will take less. It's generally advisable to leave smaller bottles, for 2 reasons. First, overfeeding is common in daycare situations, as caregivers tend to be used to formula-fed babies, who eat larger bottles than breastfed ones, and because caregivers often don't know to use paced feeding techniques, and because overfeeding can make babies more likely to need less care (e.g. holding, rocking, swapping in a pacifier for the bottle). Second, when a baby is overfed at daycare, he's less likely to want/need to nurse when he's with you, and that can be detrimental to milk supply.
So I would try taking it down to 3 oz and see what happens. If baby is satisfied, awesome. If not, you can always go back to 4 oz bottles.
Coolest thing my big girl said recently: "How can you tell the world is moving when you are standing on it?"
Coolest thing my little girl sang recently: "I love dat one-two pupples!"