Hi Starangel,
The issue with early expressing is not so much that you lose your supply, but that some babies can develop a distinct preference for the bottle to the extent that they won't breastfeed properly and then there isn't enough sucking happening to maintain supply.
For expressing at work you want to be able to get a decent amount out quickly. This usually means a double pump. Double pumps are expensive to buy, so you may want to look at hiring one. The ABA has cheaper rates than chemists, but they may not always have pumps available. If you have a fridge where you can put the milk and the milky pump bits then you don't have to wash them between pumps - just give them a decent scrub when you get home. Take a towel or a couple of cloth nappies with you - expressing can be a bit messy!
With a little one you may find that you are expressing over half a litre in a typical work day - in several sessions.
Aso - how far away from home is your business? You may actually find it easiest initially to get bub delivered to you for feeds sometimes!