the 144,000 is definately not a literal number. it is taken from the most symbolic book in the bible which even states it is written in signs and symbols.
I always found it interesting that the WT ties the 144,000 to the "little flock" which when read in context, is obviously the natural Jews only. We know the gentiles were not preached to until after Christ's resurrection when he told the diciples "go now and baptize people in all the nations", wasn't this obviously showing now the work was opened to the gentiles? I believe that is what Jesus meant when he said "I have other sheep not of this fold", also he said they must become one flock. How can some of the flock be in heaven and some on earth? Shouldn't the flock be in the same pen? Which means they have to be all together in heaven?
Also, in Revelation I find it interesting that it does not even directly link the 144,000 to being kings or priests although I do believe they are part of the church. But notice what it says about who will be priests (remember the promise to the heavenly ones to be a holy nation, royal priesthood?)
Revelation chapter 5:
9 And they sang a new song:
"You are worthy to take the scroll
and to open its seals,
because you were slain,
and with your blood you purchased men for God
from every tribe and language and people and nation.
10 You have made them to be a kingdom and priests to serve our God, and they will reign on the earth. (some bibles say over the earth)
More about the great crowd:
Revelation 7:15
And he said, "These are they who have come out of the great tribulation; they have washed their robes and made them white in the blood of the Lamb. 15 Therefore,
"they are before the throne of God
and serve him day and night in his temple;
Some bibles say inner santuary instead of temple - the place where God dwells
Oops, I guess the bible did not not confer with the WT on their teaching that this (great crowd) group are going to be just lowly servants under the 144,000 on the earth with no priestly or kingly duties, now did they?