What if everyone chose the same server?

[Quesse]

So in other words - there's a chance that you might not be able to get onto the same server as your friends, but it's all okay since we can vicariously follow each other on Lodestone?

NO. Since the timeframe for the move is so long, if a server fills up and not everybody can make it in, just choose another server. Its not like the move is happening in an instant. There will be many days for in game discussion and follow up for those linkshells/groups that want to make the move together.