Hi all Im express bottle feeding my little girl...

Hi all Im express bottle feeding my little girl - shes 4 weeks old. I found that Nagisa settled better being bottle fed. She was very unsettled being breast fed. BUT I do put her on the breast at least once a day. I usually express 160mls each time. Nagisa only drinks 120mls of the 160mls expressed. I usually put the leftover 40mls in the fridge. I have a few questions... 1. How long can breast milk last in the fridge? 2. How long does it last in the freezer? 3. If I freeze breast milk can I defrost it in the microwave? 3. Is it safe to heat breastmilk in the microwave? 4. I was told that if you dont put your baby onto the nipple then your milk dries up faster? Is this true? Sorry for all the questions, but first time mum. Thanks