Good work fella, your attention to detail is to be commended and I always love to see understated water cooled dual GPUs rigs.
Youre using Tygon R3603 right? XSPC tubing is my preferred brand but I'm not sure they do a transparent one. It has thicker walls though so it doesnt kink as easily. Personally I dont think Tygon is worth the money over some rival brands. Masterkleer is a good value alternative although it doesnt have that polished feel that the Tygon has.
The AX850w doesnt have the high pitched squeal problem that the batch 1 AX1200w has and will easily power your rig.
I'm not a fan of water cooled motherboards as I think the extra tubing makes the case interior look to busy and cluttered. Where tubing is concerned, less is more. It probably wont enhance your overclock anyway.
Cant fault any of your other ideas and if you come up witha solution to the unsightly xfire bridge let us know as I find it detracts from the overall look of my rig too.