im not on you server but was reading that you may choose server 5. When i was looking at this JPN website i noticed that server 5 has the highest JPN player going there so far(i know the numbers are small but could hold some truth statistics wise)
just though you might like to take a look before making a decision.

http://ffxiv-fan.rulez.jp/world_change.php

Also nothing against JPN players but if it turns out to be an un-official JPN server it could fill up fast