Pumping questions

I just started pumping (I know jumping on late) but I had questions that I can’t find the answers to.

1. How long do I need to pump? I feel like it takes me forever to get a flow and when I do it’s 20 minutes later

2. How many ounces do y’all store in each bag?

3. Do y’all add the milk from each breast to make enough for one feed?

4. How do y’all warm up breast milk? I don’t have a bottle warmer

I would much rather just give straight breast since I’m at home all day, but I have a hair appointment and wanted to leave my baby with my mom.