I think you can keep it in there as long as you can not drink it :icon_chickcheers: . Like all home brew its not pasturized so there will be a limit but I've been drinking some 1yr old Bottled beer recently and it still tastes fine.
After transfering into the keg I always burb out the Oxygen with 3 hits of Co2.
For extended storage I would keep and eye on the temperature, try and keep it as low as possible without freezing obviously.