Moving

[MasterTH]

in your case i would do it this way:

1. Install the new server and make him work
2. Transfer one Domain which has now priority
3. Change the DNS-Settings for that domain
4. Check if everything is working.
5. Create the other domains
6. Transfer everything thats on that domains (mail-addresses ...)
7. Change the DNS-Settings for each domain
8. Copy the Mail-Files into the right folder on the new Server.
9. Check if everything is running well, if not turn back to the old server