I would make enough juice to last 3 months. Flavors change over long periods of time so when you find your perfect recipe make no more then what you can vape in 3 - 4 months.
As far as Raw materials PG and VG can last years refriderated and if you freeze your NIC base it can last 5 or more years. You can also freeze your raw PG/VG solutions. I buy my PG/VG by the gallon and the containers are to big for the freezer so as there cheap enough I just refridgrate them.