No help for the forum noob?
D none of the above
SSD offers no benefits
the ssd caching no benefits as is slower than SSD. but if you already own it might as well do the caching with it for the OS.
the small raid 5 you have is not good enough for both media and export. better to break it up in to 2x2 raid 0 drives (need a 4th drive)
also sadly missing is a back up..