Introducing DS to the bottle today and have some question

Hi ladies,
I have a few bags frozen already and I'm plannin to feed DS with a bottle today for the first time. What is the best fast way to haw the milk? Put the bag under running warm water or place it in a container with warm water. Once the milk is thawed do I put it in a bottle and warm the bottle in a bottle warmer or do you just thaw it until the milk is warm?
If I thawed in the fridge do I pour the milk in a bottle and warm or do I warm in the bag and then pour into the bottle?
If DS doesn't finish everything in one feeding can I leave it in the fridge and feed him later or do I have to toss?
Also, do you have advice on how to avoid freezer burn? I'm using the Lansinoh freezer bags and noticed some ice in the bag...
Sorry for the million questions and I really appreciate any advice you can give me!

Re: Introducing DS to the bottle today and have some question

When I thaw my frozen milk....

I usually let it sit in a bowl of hot water. ( you can run it under hot water too, may be quicker). Then I pour into a bottle, and still try to warm the bottle in hot water too.

I know some of my bags looked freezer burned, but the milk was fine.

Those are the questions I could answer, hope that helps. Not sure how long it lasts after defrosting. We defrosted as soon as we needed it from freezer, then threw out what she didnt eat from the bag.