No i used SSD cause it is much faster then HDD because when i was building this i restarted my rig a lot of times and i didnt want to waste my time waiting for my Windows and all programs to boot but you can use HDD its up to you. I forgot to mention that SSD is using less power then HDD because there is no moving part inside.

For the power usage i dont know because i will need to take all the GPU to measure that.

And with the last question are you asking me for PCI Risers
Here is the link from PCI Risers https://www.amazon.com/gp/product/B073LNKTBD/ref=as_li_ss_tl?tag=buriedone-20&ie=UTF8&linkCode=sl1&linkId=0a10c1123b37e255d16afc6d740830d7

If this is not what you was asking can you explain because English is not my 1st language