48ci tank is enough to push a 5 gallon keg. I have used mine a few times now. I did buy a fill station for mine so I could fill it from my 40cf tank.
It is handy for making stout portable. As for regulator, if you already have a co2 regulator, all you need is a paintball tank adapter. The threads are the same and the output pressure of those tanks are around 750psi(approx same as co2)