A picture is worth 1000 words.
Here's my Weldcraft/Victor/Smith setup.
Weldcraft WP-17V with a gas flow valve (allows post flow control)
Far right, you connect the power cable to your stinger, or directly to your welder.
Center is the gas connection.
I have a Victor HVTS (two stage) multi-gas flowmeter (on the right) for my torches, and a Smiths single stage argon flow meter for back flushing when I weld stainless. This would have a separate hose connected to it run to the work piece.
For someone just doing odd things at home, I wouldn't suggest a two stage flowmeter like my Victor as they are anywhere from $250-$350 now (I've had mine about for about 25 years). Single stage would be fine, and are a lot cheaper. The Smiths flowmeter sells for about $90.
If you're flowmeter shopping on ebay, Victor's nomenclature is:
SR - Single stage
HSR - Single stage with flowmeter
VTS - Two stage
HVTS - Two stage with flowmeter
Two stage regulators will maintain a constant outlet pressure as the tank pressure decreases. Useful if you are doing a lot of welding (or cutting, applies to oxy-acty regulators too) and really use up a lot of gas in one go. For most peoples garage welding it's not needed as you don't use that much in a day and you'll shut it down and open it the next day.
A couple more tips.
For high pressure cylinders, like Oxygen, Argon, Helium and so on, you want to open the valve all the way because they dual seat valves, one to seal it when closed, and another to seal the stem when open. The gas will tend to leak around the stem if you don't open it all the way. Forget to close it and a week later you could come back to an empty tank.
These tanks can be stored and used on their sides without problem.
For flammable gases like Acetylene you only need to open it 1-1 1/2 turns.
Never use on its side as the Acetylene is dissolved in acetone and the liquid will run out the line. And if you've had it on it's side, let it sit upright for a min of 30 min before using.
The reason you normally use helium for aluminum is because it makes the arc hotter, which you need because of the thermal conductivity of aluminum. So you can set your amperage lower.
I hope, between the others and I, we've answered the questions.
BTW, I think I have one or two of the Smiths flowmeters NIB I'll sell for $60.
Smiths H1957B-580