I
vape such a low amount (3mg or less) and I haven't calculated how much I use per day but that 16 oz base lasts me for a couple years at least. Best to follow the calculator to determine how much you use in a day I think.
As for freezer life, I have some that is 10 yrs old and it is fine so I am not worried about it.
One other thing, I mix over a bowl so if a spill should occur, it can be poured into the bottle from the bowl. I only spilled it one time, I just go slow and try to be very careful.