I would personally pack EBM in small lots (say 50 ml), but give them many of them. If he's hungry after the first then they can go onto the second, but if he's not hungry then less EBM is wasted. Have a look into something like the Avent cups - they very rarely leak, can be frozen if needed, and the teat screws into the cup via an adaptor. I'm sure there are similar setups for other types of bottles too.

One thing you have on your side with pumping is that you will know what you get out - and if it drops seriously then you can take some action. The simplest action is to pump more often or add in an extra suck-feed or two. If more drastic action is needed then motilium is a medicine that increases milk production. And demand feeding on the days when you and bub are together is important.

Be prepared for night feeds to increase when you return to work as well - which if it happens will certainly deal with any supply issues, although it brings a whole new pile of fun!

Do you have a double pump? If you do it can cut the expressing time substantially, and leave you with a bit more time for other things. Also, during the day at work, just put the milky pump bits (and the milk) in the fridge between uses - then give them all a good wash when you get home. If you can collect extra sets of pump attachments (friends, ebay) it makes things a lot easier to manage as well, because then you can have scrubbing session every couple of days.