Are you sure you need the Professional Edition?

If you are looking at offering online backup services or managing distributed installations, the Service Provider Edition is probably best suited for you. Even if you have customers that only need a local (on-premise) backup solution for now, you could still use the Service Provider Edition. Of course, you can then sell these customers your managed replication services to help them ensure they have an offsite copy of their backed up data.

Please note that the Service Provider Edition and Professional Edition will not inter-operate. Hence, in the interest of manageability, it is best if you run one edition all through!