Why buy two differnt size SSD's, raid them for more speed?
Why raid the 2x4tb hdd's?
on your storage you want reliability and not speed, so Raid 0 is just stupid imo. If you are going to splash money, do it properly, get a NAS. Then you run 4x (xTB) harddrives in raid5 for redundancy.
Rest of the build looks nice! Would love to have a bit of a jam on that!