On a sidenote: We now also offer our units "barebone", just add cards! That way old/spare cards can be put into effective use with very little effort.
Had a quick look on the website but couldn't see the barebone option? What is the price
Also I know we can't see internals but the cards are using risers right?
No mobo has 13 full sized slots. So that leaves risers as the option.
The bare bones idea is good.
As stronger louder fans could be used if you don't care about noise.
I still think 10x 1070 ti's may be best way to diy this
these are the same size as the cards in mine 210mm long
https://www.newegg.com/Product/Product.aspx?Item=N82E16814500408the ones in my rig
https://www.zotac.com/product/graphics_card/zotac-geforce-gtx-1060-3gb-amp-edition#specthe 1070 tis could be set to 100tdp should pull about 1100 watts at the K-watt meter
and we know 13 1060 fit so 10 1070 ti would be a better fit.