Actually the device is called a 'flow meter' but it also acts as a pressure regulator. I have two types. One has a little floating ball inside a glass tube that is lifted by the gas flow and floats at marked increments on a glass. The other one looks like a pressure gauge and indicates flow instead of psi. Both are adjustable by a knob or a large wingnut valve handle.
The same gun/nozzle/stinger, whatever you want to call it is used for whatever wire you want to run. If you try aluminum you'll want to go for a teflon liner for the wire. It keeps the thin and soft aluminum wire from binding up in the sheath. You'll also have to run straight Argon for aluminum and reverse the polarity. I've never had a lot of luck with aluminum and never practiced enough to get proficient. Give me steel