In my experience (so may be wrong but happy to stand corrected!)...
- I express into a new bottle but then add it into the one in the fridge when I'm done expressing - it means the chilled milk isn't warming up then cooling down again etc.
- Don't think so - better to warm smaller amount then add to it, but I think once you've heated the milk up it can't be re-used
- I've been told you can kkeep it for 24 hours in the fridge - otherwise would suggest freezing it in small batches