This website is full of information about breastfeeding. www.laleche.org.uk/.
Essentially breastmilk will last a max of
6 hours out the fridge (after being expressed)
6 days in the fridge
6 months to in the freezer
Not all babies take a bottle either. Check how experienced the minder is with babies who don't take a bottle just in case.
It sounds like you really are doing this on your own, which is incredibly hard. Hats off to you. I have a 12 week old and can't imagine going it alone, never mind working too yet. I'm fretting about leaving her for 4 hours next week!
My little will be 8 months when I go back to work and I'm seriously wondering if that is too early and if I am doing the right thing....
I know you've said you have thought long and hard on it but is there anyway you could get financial help from the government and go back to work in a few months?
I imagine your hormones are still ruling your head (as mine still are!) and I worry you are going to do yourself in by working and looking after baby. Your work looking after your baby will not stop just cos they are in childcare, you be straight back to it after work-work.
Look after yourself for the sake of your child, as they need you way way more than any job does at the moment.
I want to add also how much respect I have for you and I am not judging you at all. Times are hard and I wish you all the best in whatever you choose.
Best wishes OP