Yes, you can store bm in freezer up to 6-12 months even after you place them in fridge (without freezing) for 3 days.
Yes, you need to put the breastmilk storage bags further in the freezer if you tend to open the freezer quite often so to maintain the temperature of the milk (18-20 degree celcius). If you have chest/upright freezer, it will be not problem if you didn't put the bags at the back of freezer.
Lenore Tow