If you're going to use a standing pilot and use a solenoid valve to control temperature by cutting and re-starting the main burner, you should get a flame detector like many water heaters have. I want to do something similar when we get around to making our brutus ten, but I haven't researched *exactly* how to pull this off yet.
The reason you really need a flame detector is to make sure your pilot is on before opening up the main gas valve. If you don't, you can run a lot of gas into your basement/garage/etc. without knowing it. This is Extremely Dangerous.
I'd find a pilot burner or something for a water heater instead of a pencil torch. As others have suggested, it won't work right on LP if it's a natural gas or butane torch. Another option would be to get an electronically-fired ignitor that starts to spark every time the main gas goes on...then set up your controls with a main-flame detector that's interlocked with the gas valve but has an ignition time delay.
If it sounds like I'm some kind of burner safety nerd, I am. I've played with the firing controls on equipment at work...I installed a 36 mmbtu/hr burner in our lime kiln a few years back. That could get a keggle up to boiling in about 1.2 seconds
But seriously, doing this wrong is how people blow their houses up.