You are correct that we have a higher confidence in the fire rate for gasoline cars. You are not correct in implying that we have little idea of the rate of fires in Tesla cars. We don't have '1 event' worth of data, we have '100 million miles' worth of data. That aside, yes, we should update our estimates based on future data as it is virtually certain that the numbers will fluctuate. Actually, they already have, based on there being more miles driven and no new reported fires. But few people remember to update their confidence based on a lack of events.
Yes and that includes all brands, used cars, old cars etc. Like i said, compare that with similar new cars like the new 5 Series or Benz E Series and i would guess numbers would be much closer.
If you have that data, feel free to share it so that we can compare the risk. I do not feel particularly threatened by a 'once in 4,000 years of heavy driving' type of event on a personal level, though if there were any evidence of systemic risk, I might be more concerned, though I do not own a Tesla. I also assume that there is some non-zero risk of a more catastrophic accident, which will then cause further hand-wringing, but I expect it to occur in a crash that was unlikely to be survivable or for it to involve someone doing something completely moronic. Or quite possibly both things at once and then some.
On an individual level, I am far more worried about identifying and avoiding the disturbingly large number of idiotically suicidal drivers I have met. And I mean that very seriously: as soon as I identify someone driving erratically, I find some way to get away from them, whether it means forcing them to pass me, taking an unplanned exit, or what have you, I will make sure I put distance between us.
But I remain unconcerned about a single report of a small car fire when there are many worse ones every single year (if not every day...)
Note that there have been a lot of fires in those 3 trillion miles driven by ordinary cars (not just 1), as even a quick search shows: https://www.google.com/search?q=burnt+out+car&tbm=isch