I wouldn't bother with SCSI/SAS drives for video editing, they're better suited to high queue depth random I/O situations in servers rather than the sequential I/O, single user ops that you'll get with video editing. For sequential I/O the current crop of SATA drives are just as good.
The one thing that kills video editing is I/O contention so I'd be looking at having multiple spindles/arrays with the source material on one and the output on another. Probably a couple of 2 disk RAID0 arrays to start with as well as an external backup.
By all means stick in an SSD for the OS but, as aproctor says, they're not big enough/cheap enough to use as bulk storage.