The "after this" corresponds to Amos' "in that day". The meaning is that "after this" (after the words of the prophecy were given, aka "in that day"), the tabernacle will be rebuilt (Christ is resurrected) so "that the rest of mankind may seek the Lord" (the gentiles then being called).
"In that day" referring to the day when Christ took on human flesh and walked among us, to bring the nations to Himself. There is not one hint of futurism in the passage.
"14 Simon has declared how God at the first visited the Gentiles to take out of them a people for His name. 15 And with this the words of the prophets agree …"
You’re fail to see that James understood everything that was happening in that day was the exact fulfillment of the Amos prophecy, otherwise how could he say it "agreed" if some of it was not even happening?
Reading Amos plainly, if the "tabernacle" was not rebuilt then the gentiles were not being called. But that was clearly not the case.
Amo 9:15 And I will plant them upon their land, and they shall no more be pulled up out of their land which I have given them, saith the LORD thy God.
There is no way anyone could construe this to mean this event took place in the past...
Good try -- but that's not possible.
James substituted the words: "after this I will return" for the words of Amos 9: "in that day", thus meaning that "that day" of Amos 9 would be the day when Jesus "will return".
And let's be clear -- His first coming cannot possibly be called "a return" visit. His second coming will be that day of His return.