Ok answering this on a break from classes so I got to be quick about it. Also on a cell.

1) If there is no proc, then no just keep hitting one.
2) Yes, however if your timing gets off for some reason, and it won't be ready in time to use during Wildfire, then save it for Wildfire. The same thing goes for Quick Reload as well.
3) Sushi, unless your capped on d.hit (which you shouldn't be unless you do meld) then compeste.
4) From what I've gathered it's a 3% damage increase to Overheat, however you should only Overheat during Wildfire (otherwise it's a damage loss), and only if your heat is already at like 90 or 95 when Wildfire is ready to go. If your heat is below that then don't bother.