BFers - pumping for freezer stash, questions

Summer20

Ok, so it's only been 20 months since DD was a newborn, but I seem to have mommy amnesia...

I'm (almost) EBFing DS and it's going great.  He gets one bottle of formula overnight so DH can help out and I can get a break.  So far that's worked out just fine.  I would like to start a small freezer stash though, but I can't think of when to pump.

When do you pump if you are BFing all day?

How long can you add to one bag/bottle in the fridge before freezing?

Anything else I need to know?

TIA!