[BluffTHIS!]

My Catholic perspective:

#1: Quotes from a webpage: "Rev. George Coyne, director of the Vatican Astronomic Observatory, considers the possibility of extraterrestrials an "exciting prospect, which must be treated with caution.... The universe is so large that it would be folly to say that we are the exception." Rev. Christopher Corbally, S.J., another astronomer at the Vatican Observatory, believes that if we discover extraterrestrials, it will entail an expansion of our theology, for "while Christ is the First and the Last Word (the Alpha and the Omega) spoken to humanity, he is not necessarily the only word spoken to the whole universe." Theologians have weighed in as well. Thomas O’Meara, O.P., professor of theology at Notre Dame, argues, "The history of sin and salvation recorded in the two testaments of the Bible is not a history of the universe; it is a particular religious history on one planet." For O’Meara, "the central importance of Jesus for us does not necessarily imply anything about other races on other planets.... Believers must be prepared for a galactic horizon, even for further Incarnation.""

#2. All God's creation is important to Him, all though of course humans, being created in His own image, are the most important.

#3. The quotes given in my answer to #1 indicate that most likely the revelations/religion given to us here, are precisely for us here only on Earth. This is not to say that He won't take care of them in another, similar or dissimilar, way.

#4. N/A since answer to #3 was basically no.

I want to add, and I can cite some doctrinal works on this, that it is possible that early humans/pre-humans (let's take Neanderthals for instance who belonged to the same species as ourselves but a different sub-species) were sentient but had no immortal soul. Thus, they lived & died and that was it, like you believe to be most likely the case for all of us. This could also apply to sentient beings anywhere. In answer to your obvious question why God, if all his creations and beings are important to Him, would create some sentient beings in history who had spriritual souls and some who didn't, this is all speculation anyway, and even if true, I don't know why because God hasn't revealed all about His creation to us. If He does decide to let me know in a personal reveleation DS, you will be the second to be informed, though of course you would merely take the hypothesis that I was lying or had finally lost my last marble.