Aion 2 server transfers run for two weeks. Early Access Servers go first, from the maintenance on 14 October to the one on 21 October (CEST), then Launch Servers until 28 October. Moving costs 0 Quna, you get one move per account, and you stay in your own faction and region.
Early Access characters can still only move to other Early Access Servers. If your friends started on a Launch Server and you're on an Early Access one, a transfer won't bring you together. Everything below is from NC's Server Transfer Q&A and product notice of 9 October, checked on 13 October.
NC calls Early Access Servers "Advanced Access Servers" in some notices; they're the same 38 servers that opened from 30 September.
You can leave a packed server for a quieter Early Access one in your region and faction. That's the use NC had in mind: while queues built during Advanced Access, it kept opening new servers and told players they'd "have a chance to rejoin your friends" once transfers open.
What you can't do is follow a friend to a Launch Server. If that's the plan, start a second character there instead. Each server has four character slots, but a new character starts from level one with nothing.
Launch Server characters get the second week, from 21 to 28 October (CEST), and can move to another server of their faction in their region. NC's notices only spell out the Early Access rule, so don't count on moving a Launch character onto an Early Access Server. It's one move per account, so wait until you know where your group is settling.
NC's 9 October notices set out what comes with you and what stops a transfer:
Often not. NC says "all instanced content including dungeons are available cross-server", so friends on different servers of the same faction can still run dungeons together. Where it doesn't help is the open world and your server's Market.
If dungeons are what you play together, stay put and skip the move. If you want to share the open world and a Market, plan to be on the same server, and on the same kind of server, from day one.
