I looks like you've come to this conclusion already and this may be a little late, but I was going to ask if you really needed to move the old back up over? Sounds a bit redundant to me. When assigning a new drive for TM it will create a new complete
back up of your system the first time you backup to it. Afterwards, it'll make backups of only stuff that has been changed since the last backup.
After using your new Time Capsule a while, you can check to see if your important files have indeed been backed up properly. When you feel satisfied that everything has been backed up and you have the time, feel free to delete the old backup on the old drive.