God states another fact when He says
Thus says the Lord: ‘I will return to Zion, and dwell in the midst of Jerusalem. Jerusalem shall be called the City of Truth, the Mountain of the Lord of hosts, the Holy Mountain.’ (Zechariah 8:3)
and
“Sing and rejoice, O daughter of Zion! For behold, I am coming and I will dwell in your midst,” says the Lord.
Many nations shall be joined to the Lord in that day, and they shall become My people. And I will dwell in your midst. Then you will know that the Lord of hosts has sent Me to you. And the Lord will take possession of Judah as His inheritance in the Holy Land, and will again choose Jerusalem.” (Zechariah 2:10-12)
Those aren't assumptions either, they are facts, and they will happen.
Christ’s throne is heavenly. (Rev.3:21)
Until He returns to earth with His previously raptured Bride at the end of the Tribulation:
And I saw heaven opened, and behold, a white horse, and He who sat on it is called Faithful and True, and in righteousness He judges and wages war. 12 His eyes are a flame of fire, and on His head are many diadems; and He has a name written on Him which no one knows except Himself. 13 He is clothed with a robe dipped in blood, and His name is called The Word of God. 14 And the armies which are in heaven, clothed in fine linen, white and clean, were following Him on white horses. 15 From His mouth comes a sharp sword, so that with it He may strike down the nations, and He will [d]rule them with a rod of iron; and He treads the [e]wine press of the fierce wrath of God, the Almighty. 16 And on His robe and on His thigh He has a name written, “KING OF KINGS, AND LORD OF LORDS.” (Revelation 19:11-16)
So we know from God that Jesus will return to earth, at the end of the Tribulation, with His Bride, and will begin His Millennial Kingdom. No assumptions there, just simple facts.
As are the thrones of those king/priests who would rule over the earth. (Rev. 5:10)
Yep, the Scripture does say that Jesus will have a literal, earthly kingdom and His Bride will rule that kingdom with Him.
The resurrected Jesus acts as a high priest and sits at he right hand of God. (Heb. 8:1, 10:12)
Jesus is at the right hand of God until He returns for His Kingdom:
The LORD says to my Lord: “Sit at My right hand Until I make Your enemies a footstool for Your feet.”
2The LORD will stretch forth Your strong scepter from Zion, saying, rule in the midst of Your enemies.” (Psalm 110, 1-2)
So we know that Jesus will sit at the right hand of God until His enemies are defeated at Armageddon and He returns to earth for His Millennial Kingdom.
Paul was going to be one of those heavenly kings to rule over the earth in a heavenly kingdom.
That's odd. When I look at Galatians 3:26, I see "For you are all sons of God through faith in Christ Jesus.".
Philippians 3:20 tells those who know Christ as Savior that our home is in Heaven as opposed to this earth. Since the Bible does not contradict itself, Philippians 3:20 does not negate the scores of Biblical passages that talk about Jesus Christ's literal, earthly one-thousand-year kingdom on earth.
This was a point Paul argued to the Hebrews. The Mount Zion that Christ was to rule from was the the heavenly Jerusalem, the city of the living God. (Heb. 12:22)
You quoted Rev. 19, surely you noticed that Christ and fellow judges wage war from heaven.
“14 And the armies which are in heaven, clothed in fine linen, white and clean, were following Him on white horses”
Your arguments that Christ would return to the city of Jerusalem (and what? leave the king/priests behind?) simply isn't supported in the Scriptures.