If you want multiple OS's, you won't be able to do this via the ICH (SATA controller on the logic board) if you also create a RAID. Something you should be aware of. It can be gotten around however via separate controllers (i.e. BIOS based card with internal ports can be used to boot a Windows and/or Linux installation).
If you use separate drives for OS's, you don't even need to run Boot Camp (it's just a partition tool).
I'd go ahead and stick the SSD in the empty optical bay, and use the available cable for that. You can use the following to get power to a 3.5" disk in the same bay (using the mounting kit from OWC).
- Backplane Extension Cable
- Standard SATA power cable (just cut one of the SATA ends off, and keep the other for future use if you want, and it will still work as a Molex to SATA adapter if you need, just make sure the cut ends don't short out on anything if you use it this way)
Just tie the power cable to the power wires of the Backplane extension cable (solder + heatshrink tubing, crimp connectors, or wire nuts will work - rather easy to do, as you just match up the wire colors & locations, namely for the corresponding ground, as both are black), and you get power to the 3.5" drive (data from the system's cable passes through, and attaches to the SSD). It's also cheap, and won't void your warranty, as there's no modification to any of the system's components.
As per data, you'd need a PCIe SATA card with an internal port, such as one based on the SIL3132 chip (
example - 3.0Gb/s <~270MB/s real world throughput; just as it is on the ICH in the chipset = system's SATA ports>, boots BIOS, and has drivers for OS X, and it's really cheap as well). If you want to run it under OS X, drivers can be found
here. You can still use this in a RAID if you wish, via Disk Utility (it just wouldn't boot using any disk attached to this card). Any of the other ports however, will boot OS X.
Read carefully, but this may help you understand what's possible (and why). I couldn't go into a specific setup, as there's too little information yet (you seem a bit undecided ATM, which is fine).
Hope all of this helps.