Seems like you might be using several definitions of "big"?
Snowball Earth was a big ice age. It has been suggested that we have gone through four so far with a few more coming.
in between we have had ice ages and little ice ages. You are correct I did use the term big for the last ice age because it did not result in a snowball planet just most of the surface of the Earth was covered in ice.
You talking about Orpheus theory? If so, it is my understanding that (according to the theory) THAT happened BILLIONS of years ago...and would wipe out all life and evidence of life (fossils) predating it.
Yes, it did but we have had pieces of that collision rain down on the earth for billions of years. Some of it in big chunks. This brings a thought to mind. If the collision fried the planet and the oldest rock is 4.5 billion years old the same as on the Moon then how long has the planet been here? We only have what is here, was the planet here longer than that and the Sun is older than 5 billion years old? Sorry got sidetracked. I have to re-evaluate the science.
Given that it was around the temp ranges Pluto has now, I would think the Sun would've needed to be 30 times(96%) weaker than it is today, or 15 times(94%) weaker if the Earth were somehow twice as far away.
No, only if you use a circular orbit rather than elliptical orbit. My belief is that in the elliptical caused us to have the collision in the first place. (no proof, my theory) anyway the elliptical orbit was a long one causing huge long winters twice each orbit and short mild summers. There is more to it but I am not going to get into orbital mechanics in a discussion on evolution. Hell, this is dry enough to put people to sleep.