All in one GPU coolers are quite straight forward. You install the card as normal and then mount the radiator to the chassis at a fan mount. (not necessarily in that order)
Custom cooling means: Radiator(s), Reservoir, Pump, Tubing/Hosing, Fittings, Drain and Fill ports, GPU block, CPU block, and additional fans. Even a starting CPU kit is going to set you back $200 or more. Each GPU block is nearly $100. And additional radiators have their own prices.
There are some semi-custom options. EK has a new line of quick connect water cooling systems:
https://www.ekwb.com/news/ek-releases-ek-xlc-predator-240-with-quick-disconnect/
https://www.ekwb.com/news/ek-pre-filled-and-qdc-enabled-gpu-water-blocks-are-finally-here/
EK doesn't actually have that many choices for the Titan X. Just variants of acetal, copper, and nickel plated models of the same full cover cooler. They also have their universal blocks, but they are less desirable as they don't cool everything.
I am a fan of Swiftech products. They make a pre-filled CPU cooler that you can expand to accommodate a full custom loop. I have the older model, the new one looks like it comes pre assembled with G3/4 fittings, which is nice.
And I do like a good XSPC Razor full cover block, but that is mostly personal preference. Very rare to see a round up of water blocks since it is so time and resource consuming to install them.
I think my first water cooling build to add a CPU and two GPUs took something like 8 hours to assemble, fill/prime/test, and finally get running, then another refill after the bubbles had settled out.