One must remember that terminology regarding the “Abraham’s Bosom” is not indicative of anything specific in Catholic eschatology. It’s an illustration meant to help us understand greater truths, but it is not literal. Therefore attempting to identify “a purgatory” with it would be to go beyond what the Church sees in the parable of the Rich Man and Lazarus.
It seems you are trying to do the same thing with your reading of 1 Thessalonians 4 in attempting to read St. Paul’s words as a verbatim description of the parousia. A lot of Protestants do this, but the Church doesn’t share this view for very important reasons.
The Bosom of Abraham: Not So Literal, Not So Good
On the first note about “Abraham’s Bosom,” the Catholic Encyclopedia explains that we are dealing with an illustrative device, a metaphor to explain the condition of those in the grave as part of the parable’s setting:
The metaphor “to be in Abraham’s Bosom” is derived from the custom of reclining on couches at table which prevailed among the Jews during and before the time of Christ. As at a feast each guest leaned on his left elbow so as to leave his right arm at liberty, and as two or more lay on the same couch, the head of one man was near the breast of the man who lay behind, and he was therefore said “to lie in the bosom” of the other. It was also considered by the Jews of old a mark of special honour and favour for one to be allowed to lie in the bosom of the master of the feast (cf. John 13:23).–The Bosom of Abraham, Catholic Encyclopedia, New Advent.org.
A plain way of translating “Abraham’s Bosom” is to say that Lazarus was “sitting in the most honored place,” as at a feast. Of course this wasn’t a feast, but death, and it was a state wherein the Beatific Vision was not accessible. Thus the Catechism describes “Abraham’s Bosom” as a state of deprivation:
Scripture calls the abode of the dead, to which the dead Christ went down, “hell” - Sheol in Hebrew or Hades in Greek - because those who are there are deprived of the vision of God. Such is the case for all the dead, whether evil or righteous, while they await the Redeemer: which does not mean that their lot is identical, as Jesus shows through the parable of the poor man Lazarus who was received into “Abraham’s bosom”:“It is precisely these holy souls, who awaited their Savior in Abraham’s bosom, whom Christ the Lord delivered when he descended into hell.” Jesus did not descend into hell to deliver the damned, nor to destroy the hell of damnation, but to free the just who had gone before him.–Catechism of the Catholic Church, 633.
The Catholic Encyclopedia also explains that since the first century, among Christian writers “the Bosom of Abraham” has “gradually ceased to designate a place of imperfect happiness, and it has generally become synonymous with the Christian concept of Heaven itself, or the Intermediate state of existence” between one’s death and their Particular judgment and the upcoming General or “Last” judgment after the resurrection of the dead. But this latter definition is not dogmatically binding nor applicable to the direct reading from Scripture from which this expression derives.
Purgatory, though a Jewish concept of the time, is not mentioned in connection with the illustration in Luke 16. Since placed in the setting of Hades, Purgatory does not feature in the metaphoric Bosom of Abraham since the “Bosom” itself is in Hades or “hell.” Purgatory and Hell are not synonymous.–See CCC 1030-1037.
Since the illustration of Luke 16 is a parable, Catholics should not expect the metaphors to supply a literal window on death.
1 Thessalonians 4: A Teeny-Tiny Apocalypse
It would be unwise to take the metaphors used by Jesus in the parable of the Rich Man and Lazarus and force-fit them into St. Paul’s words found at 1 Thessalonians 4:13-17.
The main reason is that the Church asks us to read the Bible on its own terms, which includes accepting the genres or narrative devices used by the readers instead of demanding that every part of Scripture be as literal as an encyclopedia entry.
The Ignatius Catholic Study Bible explains that Paul was employing apocalyptic imagery in these verses, using terms from Exodus, Joshua, and Daniel to depict the coming of Jesus at the end of time. (See that volume’s commentary on these verses for more information.) Since, therefore, the parousia will not consist of a literal fulfillment of these verses, your questions don’t have a literal answer.
The context for these texts? The* Ignatius Catholic Study Bible* explains:
Apparently some were concerned that the faithful departed would be left behind when Jesus returns to bring the [living] saints to heaven. Paul insists otherwise: the righteous dead [those the Lord ‘brings with him’] will be raised in glory and gathered to Christ even before the final generation of believers still living on the earth in the last days [those ‘alive at Christ’s coming’].
Paul follows this up with imagery associated with the fiery cloud of Mount Sinai, the trumpet blast that brought down the walls of Jericho, and the Messianic Son of Man vision of Daniel to instruct readers using apocalyptic narrative that spiritual union of the faithful departed with the Lord precedes the parousia which occurs at history’s end.