Dear Kevin,
You need to install both of them BE 11d and BE CPS. You can install it on the same machine or on separate servers. Note that for BE CPS you need at least 1GB of RAM.
For CPS you can use only to disk backups, but later on, you can move that backups to tape (disk to disk to tape). This is same for all CPS (file server, Exchange or SharePoint). For Exchange, you have to do full backup first, and then CPS will backup transaction log, but it is recommended that you periodically do a full backups (for example, once a week - depending of quantity of data in you Excahnge).
Best regards,
Vladimir