1. It totally depends on the style of roast you want. If you want a dark roast, youll go past the second crack. Alternatively, a lighter roast, youll need to settle just before the second crack(?)
2. Youre right with the first crack, its fairly audible. However, the second crack isnt so audible. Youll need to listen closely, but its more of a snap/crackle/pop like with rice bubbles.. Its not as loud, more like a split ;D
3. You should have a stop watch/timer and time your roasts, record the time, temperature, etc, and compare the results and tastes. This makes it easier to roast to a certain degree next time, and youll have more consistent results.
4. It shouldnt wreck it. However, I dont have a Gene Cafe, so Im not sure what the emergency stop involves. If it just stops the machine and allows you to drop the beans, then I cant see a problem..
5. Not sure, totally depends on the bean and your style of roasting. Cant help you there Im afraid!