The Vcc _must_ be supplied with a regulated 5V - anything above 7V will destroy the chip (abs max ratings). Italso need standard logic decoupling of course.
Heat dissipation to a first approximation is about 1 to 1.5 times the current - the saturation voltage of the darlingtontimes its current.However since this is a high voltage switch there will be significant power dissipation on switching (switch off takes upto 25us) - if the output voltage is 100V at 6.5A then a smooth ramp-down could dissipate about 8mJ, or 8W at1000Hz... Output voltage depends on the inductor being switched. Only at switch-off will there be a high voltage (inductive load).
That's the one - the actual voltage depends on the ignition coil primary and secondary and the spark-gaps.
Were I you I would look for some app notes on the product. Might help a great deal.Bob