I want to replace my current TimeMachine backup disk with a new disk, but I also want to copy the existing contents to the new disk after encrypting the new disk.
How can I best do that? Are there any pitfalls waiting for me?
Apple has some instructions in this KB. There are some restrictions - Apple suggests that you'll need to format the new drive as
Follow the other instructions in the KB, and you'll be able to use your new drive as the TimeMachine drive.