Makato333

Pretty standard pick for high performance, low noise on tight and small cases/builds.

Using fiber instead of ethernet cable won't help you because they'll have the same latency and speed... your problem is not the cable, but it's the actual encoding of the image into some compressed stream which gets sent through the network cable and then decoded back into raw image... it's unavoidable to have some ms worth of delay.
 
You can buy HDMI cables that use fiber to carry the signal ... basically, they have chips at both ends which convert the hdmi signal to light that goes through fiber, and then at the other end the chip reads the light and converts it back to hdmi
Here's an amazon page, can't tell which one is the best: https://www.amazon.com/s?k=hdmi+fiber&ref=nb_sb_noss_2
There may be HDMI cables or DisplayPort cables that can do 30ft or more without using fiber, basically they have either a strong amplifier chip on one end sending a higher power signal through the cable, or somewhere in the cable they have a "repeater" chip which picks the weakened signal and re-amplifies it
 
Here's an example of a 50ft DisplayPort cable with a built in boost processor to amplify signal (note this particular one I think it's limited to maximum 2560x1600): https://www.amazon.com/DisplayPort-Cable-50-15m-Active/dp/B00EG3YA2G/
 
Here's a 50ft HDMI cable that claims it can do 4K ... cheap at 30$ : https://www.amazon.com/Cable-supports-FullHD-Ethernet-KabelDirekt/dp/B008U7SLJW/
 
There's also USB cables that are longer than 5m, and usb cables which use fiber to get long distances (with such cases you need a powered USB hub, you basically use the fiber usb cable just to transfer DATA between pc and usb hub, and the usb hub powers everything (keyboard, mouse, gamepad etc)

I got a G12 on the MSI 1080 Ti Armour with a Kraken G42, thats a 140mm Radiator https://www.nzxt.com/products/kraken-x42
it runs the Card at below 40C for hours when Gaming, no need for the 360

Yes, it's compatible but the x72 is more than a bit overkill. A 120mm AIO is plenty already. 
Example here: https://www.reddit.com/r/buildapc/comments/6cq96e/infokind_of_kraken_g12_does_fit_on_1080ti_and_my/

I do not know for 3, but i have seen for 2.
Then just get 2 mounts

You're much better off just buying a few single arm mounts. Plus it lets you position them where ever you want.
This kind of set up doesn't make sense for a multi arm stand.
 
Welcome to the forum!