I have heard that their where 600 000 souls created and those are the souls that where at har sinia. Does that mean that all the millions of jews born after har sinia are a reincarnation of those same souls. how are we to understand this statement? What happens when there will be the coming to life of the dead, will only 600 000 souls come to life?

To fully understand the true notion of souls and reincarnation one has to be on a certain cabbalistic level which I am not on yet. The soul is an extremely complex entity, much more than the body, and one should be very careful of simplistic childish misperceptions of the spiritual. 600,000 is a significant number in Jewish thought and it connotes figuratively to the whole entire Jewish people.