See, that makes a difference. You only have 1 eSATA port available, but have several SATA ports.
IMO, I would [with this mobo] build an internal RAID 1 system on the SATA ports for mirrored data/backup with a main OS HDD on an additional SATA. If you want OS/app speed, then get an additional HDD to run the OS in RAID 0. [this is assuming your processor is worthy of such an array]
Then, I'd add an external hotswap cradle backup system on the eSATA to offload a backup once every two weeks. This way, you have your data in three seperate places - mirrored inside the computer in case of failure and an external that you can guard from fire, theft, etc. The external eSATA will fly when it comes time to offload.
There are plenty of options really. This is only one based on the single eSATA availaility and speed.
Personally, I run RAID 0 OS on two Raptors, a third HDD for data/backup and an external HDD for mirroring [non-RAID] my backups. I'm swapping the external to a hotswap very soon myself. All of them are eSATA and nice and fast.