My $.02 on SRT. I have a PC with a dedicated SSD to cache data and the difference between it and an identical drive in the same system is not noticeable. But to answer your questions...
1 and 2) Yes. Any mSATA SSD should work. However, I think that you are better off getting a 2.5" SATA drive. You can easily transfer it from PC to PC if you need/want to in the future. I personally would say skip caching and get a regular 120GB or 256GB SSD and call it a day.
3) It won't be a problem but from my recollection you can only cache one drive. So you will have to pick drive C or D.
Here's a quick search of mSATA SSD drives
from Newegg. Here's a quick search of regular 2.5" SSD drives