Breast milk has the rule of threes. Three hours out of the fridge. Three days in the fridge. Three weeks in a built in fridge freezer and three months in a proper freezer.
You can get bags to store the milk in that doesn't take up heaps of space when you put them in the freezer. My mum told me not to store milk in the fridge door, I can't remember why but think it has something to do with not getting cool enough.
Put it in the lansinoh storage bags specifically for breast feeding, then label it and stick it in the freezer.