How to know how much milk to store?

Hi everyone! I had a few questions I was hoping someone could help me with. My son just turned 7 months old, he is currently ebf with no bottles currently. I'm planning on going back to work in the next few weeks (full time) so once my pump comes in, I'll be starting to store a freezer stash. My question is, how do you know how much milk you should store in each bag? And typically, how many oz per day do babies this age eat? My son usually eats every 2 hours, sometimes 3. I have heard about the 1oz-1.25oz per hour rule, but does that mean for example, if he goes 4hours without eating, to give him 4oz+ at his next feeding? Sorry, I'm just so confused!