I'm using a regulator in to my gas beam, then a shutoff ball valve at each burner, which goes in to a 1/2" black iron "T" - One end of the T goes to a needle valve to reduce pressure to the pilot light, and the other end connects to an electrically operated Asco fuel gas valve, then through a bell reducer to a needle valve to control flow to the burner itself. I guess with fuel gas you're supposed to use bell reducers instead of hex bushings, but I'm using a hex bushing to reduce 1/2" to 1/8" NPT for my pilot needle valve. Looks like this currently:
EDIT: I guess it would be helpful if I responded to your questions
Has any one used 1 regulator per burner?
Has any one used the valves from a gas grill to control each burner?
I didn't. A regulator's job is to maintain constant downstream pressure with variable upstream pressure. Since upstream remains constant from my regulator, I'm using needle valves. I'd imagine that the valves in a gas grill are needle valves due to their exceptional fine flow control.
How well does the gas shut off valve work to control the flow of gas?
Ball valves don't regulate gas flow very well for fine control... my pilot needle valve drops pressure from ~15psi to less than 1 psi. That would be a challenge with a ball valve.
Could the parts from a old gas range be used to control the flow?
Perhaps, but I've never looked at what parts are in them.