PP is not something that will be used in any way during fallout. It's just convenient for explaining transform's mechanic. As far as I'm concerned, copycat and mimic can last indefinitely though most users should have trouble retaining mimic/copycat through sleep. (Psychic/Ghost types should be able to retain mimic past sleep, not that ghost types are known for sleeping.)
And yeah, that's more or less correct. I don't think that hyphen in the middle is grammatically correct but the name is right.
And... yes. Almost every pokespirit was once alive before the virus hit. They would also remember the old days, and could relay this information to their wielders verbally. (Pokespirits are capable of mental communication with their wielder, but no one else.)