Need adivce: moving from stock IMAP server to Cyrus IMAP. How hard is it?

[Apollo's list account]

My users like to keep 500 to 1000 messages in their mailboxes and 
average about 500K per message (we are a talent management company, so 
there is lots of multimedia being exchanged).
So far I have been running whatever came stock with FC1, so I have 
Postfix with WU IMAP running in that standard UNIX mailbox mode.

Can I keep Postifix and just change it to Cyrus IMAP style mailboxes and 
install Cyrus IMAP? Or do I have to start from scratch?
Fortunately I have only 10 users, so I will have to deal with about 10K 
in messages and about 150 sub folders.