1) voltage depends upon the manufacturer of the ignition unit, but most are 4.8 V. A gas engine with a magneto ignition does not need any battery at all.
2) see (1)
3) A typical receiver battery is fone for ignition. Needs about 800 - 1200 mAh capacity. perhaps more for a twin.
4) this is a function of the oil, not the engine. Typically 30 - 1 or as much as 100 - 1.
5) close choke. turn on ignition. throttle at fast idle. flip prop until pops. open choke. flip prop until running. about 10 or 15 flips total
6) wiring for electronic ignition is simple. battery to switch (with charging receptacle) to ignition unit.
&) gas is probably "easier" and more reliable than glow in the long run. glow engines tend to be more tempermental.