H A Believer,
Again, what does the great crowd have to do with what God will do for the Earth? You are assuming that ONLY the GC can be on Earth.
Who are they? Who knows. You'll find a million different interpretations online.
Where are they? Heaven.
What does this mean? WT is wrong
What hope is there for the Earth? Again, who knows? Another million different theories online, all based on different biblical interpretations.
If you want to be Christian, there are only a few things which are certain: You must put faith in Jesus and love your neighbor. Everything else is open to interpretations and very unclear.