I have no answer to the second question, but the answer to the first is that there is no real scriptural basis for Rapture theology. Those who believe in it point mainly to this misinterpreted verse in Thessalonians:
1 Thessalonians 4:17 “After that, we who are still alive and are left will be caught up together with them in the clouds to meet the Lord in the air. And so we will be with the Lord forever.”
The phrase that I bolded, “caught up together,” is one word harpagesometha (literally “caught up together”) in the original Greek.
The verse appears in the Latin Vulgate as thus (with the relevant phrase bolded):
“deinde nos qui vivimus qui relinquimur simul rapiemur cum illis in nubibus obviam Domino in aera et sic semper cum Domino erimus”
The word rapiemur, above, is a future tense form of the Latin verb rapere, which means “to seize, grab, carry away.” The future perfect tense of the word is rapturus. The term, “rapture,” therefore, is derived from the Latin.
This verse represents an answer Paul was giving to people who questioned whether those who had already died before Jesus came back would still be able to go to Heaven (this was at a time when people still believed that Jesus would return within “this generation”). Paul was telling them that not only would the dead go to heaven, they would ascend before the living. He was talking about the second coming, though, not a preliminary ascension before a “tribulation.”
The whole rapture theory was largely the fever dream of a nineteenth century preacher named John Nelson Darby. Darby conflated the verse from thessalonians with this from Revelation:
Revelation 3:10 “Since you have kept my command to endure patiently, I will also keep from you the hour of trial that is going to come to the whole world to test those who live on the Earth.”
and this one:
Revelation 20:5,6 5 But the rest of the dead lived not again until the thousand years were finished. This is the first resurrection. 6 Blessed and holy is he that hath part in the first resurrection: on such the second death hath no power, but they shall be priests of God and of Christ, and shall reign with him a thousand years.
From those three verses, Darby got the notion in his head that the good people were going to get raptured (“first resurrection”)and the bad people would endure a period of “tribulation” before the “second resurrection.”
This was a new theory, as formulated by Darby (based partially on the visions of a schzophrenic teenage girl), and was really never really a part of any Christian doctrine before him. It is still not accepted by most Christian churches. It’s really sort of peculiar to American fundamentalists.