You can't easily scale that from your home recipe so what you'll have to do is figure it out in the commercial kitchen. Which is easy as long as you keep an eye on it. Whatever pot it is in, that should be the same every time. Temperature also. On your first trial if you reduce for 25 minutes and it tastes perfect write everything down. A spreadsheet can help.
True, assuming you can apply heat at the same rate every time. With a gas burner, that can be problematic. I've discussed with the facility manager installing a mass flow controller on the gas line for the gas burners I use to make my pepper candy. So far he hasn't been receptive to the idea.
Measuring temperature and time can get you pretty close. I make the PMS sauce in a steam kettle with an integral thermometer and pressure gauge. Monitoring those and time gets me pretty close, but I still verify with a Brix measurement.
What is the best way of going about contacting an FDA Agent or should it be fine to go through my Processing Authority?
Go with your PA; they may be able to help with the best end point determination, too.
You can also measure your reduction with a stick ruler.
What he said. As long as you use the same kettle every time, that's probably going to be the most effective way.
Plants are people, too.