Is it best to keep the co2 cold or warm
should the tank be in the cold or can it be outside the cold storage
When carbonating the beer and when drinking the beer
Doesn’t matter with the CO2. I keep mine inside the kegerator to keep myself from tripping over it during those slightly drunken’ trips to get another pint.
Do whatever you think is easier. You get slightly more out of the tank if you keep it warm, but I don’t think it’s enough to worry about. The only caveat, it helps if you keep your secondary regulators warm, they start acting up (taking a long time to normalize) when they get cold. For that reason, I keep my tank and regulator bank on the outside of the fridge.
should CO2 be cold or warm when carbonating keg?
YES!
really though, doesn’t matter. suit what works best for you. the C02 will be fine either way.
My 20lb CO2 tank & regulator are in my fridge.
It’s basically 'cuase I have a big display fridge (3 glass doors) and it’s just easier for me that way. It’s never been a problem.
I keep mine in the fridge and haven’t had a problem yet. I think it was mentioned before, the regulators act a little funny, but at least in my case, they consistently act the same way 
I just moved mine to outside my keezer for two reasons. One, my regulator measures differently in the keezer (lower) as opposed to outside the keezer and I really couldn’t get a good read on it to determine whether or not I needed more CO2.
Two, and the most important, there’s more room for beer now!
Cheers!
The high-pressure gauge will change any time there’s a change in temperature. No matter what temperature it’s at, it’ll start dropping once it’s about 10% full.
In the keezer it read in the red like I needed more CO2. Outside of the keezer it reads above that at least giving me a decent indication of when it’s running low. Either way, it works to carbonate your beer, it’s just easier for me to read outside and refill the tank without moving around kegs.
I guess different manufacturers put the “red zone” in different places. On my regulators it’s at 300 and 400 psi, either of which would be well below freezing. Regardless, all I meant was that it doesn’t matter what the gauge is reading - until it starts dropping you have plenty of CO2.