I walked away from a career I loved, had spent a lot of money and 10 years of my life preparing for (I'm a veterinarian) and was very well paid in order to stay at home with my first child. It cut our income in half, and we don't live where it's cheap to live.
It can be done. We do without a lot of stuff, like cable TV, high speed internet, eating out, all kinds of nice stuff, but we have the basics covered plus a little.
I did start picking up PT work out of the home when my oldest was 18 months old; before that, I watched a neighbor's baby to just make a little pocket money for me.
Are the extra things your income buys worth missing all the firsts? That's what did it for me. The money is nothing in comparision to my children.
Good luck deciding what to do regarding going back to work or not.
For starting a stash, I would just start pumping a little bit every day and build up a day or two's worth of milk. Then, once you are back at work, you pump the next day's supply while away from your LO.