Turning to Revelation 5:9 it mentions that God selected his kings and priests from "every tribe and tongue and people and nation." Are these the same 144,000? Yes, because the verse says that they are singing a new song before God.
Read Revelation 5:9 in context. Those singing the new song in this verse are not the 144,000 - it is the 4 living creatures and the 24 elders.
On the one hand, it says that this exclusive group of 144,000 is taken from all tribes and nations, but then the passage you noted says they are taken from the 12 tribes of Israel
Again - not correct if read in context. There is clearly more than one group in heaven - Revelation mentions at least 4 different groups (not including the angels, the 4 living creatures, Michael, and Jesus) - there are (1) the 24 elders, (2) the 144,000, (3) the saints, and (4) a great crowd. And note - that the great crowd (Rev 7:9) is standing before the throne of God in heaven.
On another topic - the Diety of Christ - Revelation offers an interesting insight. Notice Rev 1:12-18. Someone like the "son of man" is speaking, who says he "I am the first and the last, the living one who died and I am alive ever more" - obviously Jesus. However, Isaiah 44:6 (NWT) says "This is what Jehovah has said, the King of Israel and the Repurchaser of him, Jehovah of armies, 'I am the first and I am the last, and besides me there is no God'..", and again Isaiah 48:12 Jehovah calls himself the first and the last, now Revelation 1:8 according to the NWT says "I am the Alpha and the Omega", says Jehovah God "the One who is and who was and who is coming, the Almighty", Rev 22:12-13 "Look! I am coming quickly...I am the Alpha and the Omega, the first and the last, the beginning and the end."...who is talking in Revelation 22:12-13...read further to verse 16 - it is "I, Jesus".
Both Jesus and God refer to themselves as the First and the Last, the Alpha and the Omega. It is obvious to me that only one can be the First - and only one can be the Last - there is only room for one. Revelation 1:7 tells us that Jesus is coming, yet the NWT in Revelation 1:8 tells us it is Jehovah God that is coming - so who is coming?
Read John chapter 14, Philip asks Jesus to show him the Father, Jesus answers (verse 9) " Have I been with you so long, and yet you do not know me, Philip?" and in John chatpter 20, verse 28 Thomas calls Jesus "My Lord and my God".
You Know - I struggled with this concept for a long time - being raised a JW I could not understand nor accept the Diety of Christ. However, once I read the book of John and the book of Revelation by themselves it was all too clear that Jesus is God.