1. You really don't need to preheat, but it's like chicken soup. It doesn't hurt. You only need to hold the steel at heat for 10-15 minutes. The times in the manuals are for thicker sections. Tempering twice at 400F should give you about Rc61-62.
2. Yes, though you want it to cool itself as quickly as possible after the hardening. Cool airflow works.
3. Blow hard (joking), but not from one side. You need both side to cool evenly. A fan running the length of the blade is OK. When the steel is just cool enough to handle is the time you want to straighten out the warp. It's pretty maleable and you can fix your problems there.
4. D2 hardens at 1825-1875F, and you'll need toolwrap or something else to protect it or the steel will decarburize.
5. See 4
6. See 2 & 3
7. Dunno. Most folks do this in temperature controlled ovens with a thermocouple.
71 is no excuse!
