Going back to work

At the end of this month I am going back to work and have been officially breast feeding for 2 months. I would like to continue to breast feed but am scared ill lose my milk. I have been pumping 2 times a day for about 10 minutes each time to store and freeze for when i do go back. My question. Is how often should I start pumping and for how long and how much milk should I have for my 2 month old for while I’m at work?