Nice post with a plethora of information and exquisite questions. I have a fairly simple definition of life, it is all contained in that simple but complex twisted ladder shape. If it contains DNA it is or was at some point alive. I don't know of a better way to classify life.
Thank you @coinsandchains :-) It's difficult indeed. And then we're only talking about live as we know it. Who knows if there's other forms of life as well? Silicon based instead of carbon based... ? Who knows?
Silicon-based? That would be really interesting, which does bring another aspect into living things, why always carbon?