Hey, Milo- what an incredible project! I've been busy moving to South Carolina from Arizona, so I haven't had the time to read much of the stuff below all the coffee buying forums (never want to miss out on good green!). Anyway, I couldn't see where you've found a solution to controlling the heat from 1st crack. Over the years, I've noticed the toughest thing in monitoring roast profiles is placement of the probe, and I think everybody commenting in most coffee forums (coffeegeek, home-barista and here) report slightly different temps (varying by as much as 20 deg F). I think that's owing to the type of technology they're using (maybe roast batch size as well). I use J-type TC's in my sample roaster (US Roaster Corp) and a datalogger from Picotech, and typically start to hear 1st crack around 380-390 deg F on the bean mass probe (the only one I log), and start dialing down the flame there.
Interesting project-- makes me want to go back to school just to learn the acronyms and neat electronic doo-dads!
Ray