You don't 'need' a RAID card for anything.
A RAID setup can:
- provide some level of safety by providing redundancy in case a drive fails
- provide a performance increase by spreading reads and writes across multiple drives.
You usually clone the OS and apps only to SSD.
SSD is useful for audio, can be used for scratch where you are short RAM for CS5.
A WD Black 1.5TB $108 is fine, maybe a couple.
Software stripe RAID for editing, one for system, and for backup - you could go with WD Green 2TB for backups.
http://www.macperformanceguide.com has a "slew" to tips on hard drives, upgrading, and configuring - and Hitachi Ultrastar 3TB. You should look over his site.
First and foremost, clone and clean up and repair, even erase and restore from clone, with your current system and figure out why or what is wrong now.
People buy $$$ ! SSDs then want to limit the writes to preserve the life of the cells and the performance. I feel they are tools to be used.
You never want to leave just the OEM hard drive, or leave other hard drive bays empty. Use 'em.