1Peter3:18 explains perfectly that Christ did not return from death in a physical body. The resurrection after 3 days was in fact a spiritual reality.
As for Jesus being the first resurrected to life, life in this case is to fully spiritually aware, it's spiritual life, so Jesus was in that sense resurrected while still alive, after death His spirit entered the spiritual dimension already resurrected in life. All humans have a spirit, this is referred to in Genesis when it is said we are made in the image of God, not capable of reflecting the attributes of God, though this is also possible.
The image of God is spirit and we contain an aspect of the substance of God. Everybody after death enters the spiritual dimension and ascends to the degree they have made themselves worthy of.
As for the 144,000, good luck with that. There is no suggestion in the Bible that 144,000 individuals are more worthy than the rest of humanity. The passage speaks of a new song, which means a new religion and the 144000 has a complex numerical and symbolic value related to peoples from all tribes in great numbers turning to this new religion. The least likely interpretation is that God needs or will seperate 144,000 individuals to rule with Him.
Interestingly the Jehovah Witness who have nominated themselves, no less, to rule with god substantially exceeds the seating arrangements. Doesn't that tell you have illogical this belief is?
The righteous who will possess the earth are the generations that will live morally in the love of God, generation after generation. Physical death will remain a constant.
