to determan what size tank you will run you will need the means to fill it efficently. so if you have a 12 gallon you would need 4 viar 450s to make it efficent (IMO) or a engine drive compressor.
the the more volume and pressure to reach the more compressor you will need.
the connections between tanks with the lecking....thats Bull shit. the entire set up consists on connections and the proper install will yeild no leaks. so if you want or need multi tanks, do not be afraid to do so. leaks are not hard to find and fix.
my car has set for a week with out moving, and when i went to drive it, there would be the same pressure i left it with before i parked it.