On point 3, yes, planets are literally "wanderers" whose celestial motions as viewed by humans on earth do not follow the uniform order of the stars. It's their unique transit through the heavens that makes them different from stars, not their composition.
Because otherwise planets still look like specks of light to the unaided eye, so that before the telescope their true nature wasn't known. And their full number in our solar system wasn't known, either, since the more distant planets couldn't be seen.
The "Big Bang" theory of the universe only brings us back in time some billions of years ago. What precedes the Big Bang is unknown, and it's possible to speculate that countless consecutive Big Bangs have occurred over trillions of years. But as it's presumed nothing tangible would survive from the previous incarnation of the Universe during a Big Bang event, no one expects to find evidence of prior universes.
It appears that for now, with our current knowledge, what we see is what we've got.
As for life on Earth, I think it's entirely possible to be the result of colonization by space microbes, that arose in some other part of the Universe. Or even a mix, of indigenously occurring life, and extra-terrestrial life. That idea is actually not new, and was already forming the basis of novels like HG Wells' "In the Days of the Comet" published in 1906, well over 100 years ago.