The two largest factors in juice life span are the nic level and the ingredients used in the flavoring - the latter of which is a huge variable.
PG in itself is a virucide and bactericide, so storing unrefrigerated shouldn't be an issue.
It's safe to simply refrigerate until you're ready to use, and avoid purchasing too much in advance. I usually keep no more than a few hundred ml's on hand, personally.
As I understand it, the general rule of thumb is that you can store most juices for about 18 months without issue; beyond that, the nicotine starts to degrade significantly. I don't know how freezing impacts this, though.