Preparing bottles for back to work

I go back to work Monday 🥺🥺 my baby is 3 months old . I will be pumping at work but I’m wondering how to get my mom set up for bottles ???? For Monday at least I’ll be using my frozen stash . I’ll be gone from her from about 830-530. And I plan on feeding her around 7 /730 before I leave. I’ve been feeding my baby on demand and she doesn’t really have a set schedule; some days she’s cluster feeding.. other days she eats maybe every 2/3 hours … some days it’s every hour. How should I defrost and make bottles and how many ounces should I take out ??? Also when should I put the frozen milk in the fridge ? I appreciate all and any advice !! This has me super stressed