1) Jayz2cents is a good site. He has a few videos on water cooling.
2) as said, PCPARTPICKER is a good start for finding a case. Probably one without a front DVD would be needed based on your liquid cooling desires.
3) however, I would avoid multi-GPU and frankly the amount of RADIATOR you are looking at seems pretty excessive. A single, 120mm radiator is plenty for a GTX1080Ti, as the Hybrid models stay near 50degC at normal ambient room temp.
And a modern CPU doesn't need a thick, 360mm radiator either.
4) Ever see the Terry Crew PC build? (it's massive overkill on the CPU etc but it's pretty cool)
https://www.youtube.com/watch?v=VDZNXRAtXs0
5) as I said before, GSYNC is what you want for a high-end build with a single GTX1080Ti
6) 4K is not a good way to go for gaming. The Hz (thus FPS) is limited and the increased pixel count doesn't produce enough visual benefit to justify the loss of smoother gaming.
Of course you can set a game to 2560x1440 and have it scale, but that doesn't help with the max FPS to keep in the asynchronous range for smooth gaming (i.e. 30FPS to 144FPS).
7) Asus Strix GTX1080Ti (air cooled) has RGB lighting and can control case fans. You might consider making just a CPU loop with a 240/280mm radiator which still looks pretty neat.
If you do go with a GPU loop, choose the pump carefully. Some have noise issues. I'm not sure if you want a full waterblock or hybrid solution.
Not sure if you are aware, but water cooling won't really help gain more performance. All the GTX1080Ti's get roughly the same once OC'd. Lots of info on that including Gamers Nexus but the main reason is that too many people damaged their cards so NVidia started locking the voltage down. (it wasn't just consumers, but there was a "race to the bottom" with Asus and others to eek at the last few percentage gains but lifespan was dropping under one year so NVidia stepped in and said. STOP. just stop.)
SUMMARY:
It's really easy to throw money at a PC build because you want "the best" which a lot of people think is a 4K rig, but I disagree. Again, avoid multi-GPU and look at a 2560x1440, or ultra-wide 3440x1440, GSYNC monitor.
That's my two cents.