It should be fine but you don't want an IP change during a backup. In ClearOS you will want the FTP server and probably the Flexshare app. Also you will want to activate your free Dynamic DNS which comes with ClearOS. You will get a subdomain of poweredbyclear.com. It will allocate one to you but you can change it so something more memorable if it is not in use by someone else.

Backing up by ftp will be somewhat heavy-handed compared to what you can do with rsync which can be set to skip any file already backed up but you would need to script it yourself. Alternatively you could look at the BackupPC app which, I believe, also uses rsync. This should minimise the time needed to do the backup and the data volume.