DNS Cluster / Account transfer

This is possible. A few comments if I may from my own experiences doing this.

Don't delete anything, anywhere until you're sure you are done.
Make sure DNS cluster works properly in advance of moving anyone.
New server, new server host name, so, users that have been using theirdomain.com/cpanel and been redirected (via Tweak settings > Redirection tab) to old.server.com will now be going to new.server.com and this is fine of course, but if they've bookmarked cPanel once they're logged in, old.server.com will no longer work at some point so, users won't get in and will be contacting you.
Setup the DNS cluster proper and move one of your own smaller accounts or test accounts to make sure all works as expected.
If you have large accounts near quota, this could be problematic during the move. To insure its not, change the quota on those accounts and give them plenty of space in advance of moving them. You can reset to the default account quota once you get them to the other side.