Help Selecting PC Parts with Budget ~2k

I think you are on the right track and Hellfire suggested some really good components. There is not much to comment on there.

As far as cases are concerned, the Phanteks Enthoo Lux is a really nice case and it will handle the H150i without a problem. The Fractal Design Define R6 is a really nice case as well. You really cant go wrong with either of them.

I would also ask, what monitor are you using? With a build like this you should get a really nice monitor to go along with it. At a minimum you should get a 1440p/144hz panel. It will scream on your 1080ti. They are expensive, but ultrawide monitors are incredible. I have the Predator x34 and cant say enough good things about it.

You have a great start finding a GTX1080ti available for what I hope is a reasonable price.
Your budget will permit the following:
1. i7-8700K.
2. Noctua NH-D15s cooler
3. Seasonic focus 650w psu.
4. 2 x 8gb kit of ddr4 ram. speed is not important, look for 3000 to 3600
5. Any Z370 motherboard will be good. No need for luxury models.
6. Samsung 960 evo m.2 pcie ssd; 500gb is good.
Unless you will be storing large files such as videos, why not defer on the hard drive until you need the space.
Then, I think I would look at WD red/blue/green since performance should not be important for such uses.
7. Cases are a personal thing, and most will do.
Pick one you like the looks of; you will be looking at it for a long time.
My personal criteria is at least two 120/140mm front intakes that have a washable filter to keep your parts cool.

Look these up and put together a list with links to verify that all is good.

FWIW:
My canned rant on liquid cooling:
------------------------start of rant-------------------
You buy a liquid cooler to be able to extract an extra multiplier or two out of your OC.
How much do you really need?
I do not much like all in one liquid coolers when a good air cooler like a Noctua or phanteks can do the job just as well.
A liquid cooler will be expensive, noisy, less reliable, and will not cool any better
in a well ventilated case.
Liquid cooling is really air cooling, it just puts the heat exchange in a different place.
The orientation of the radiator will cause a problem.
If you orient it to take in cool air from the outside, you will cool the cpu better, but the hot air then circulates inside the case heating up the graphics card and motherboard.
If you orient it to exhaust(which I think is better) , then your cpu cooling will be less effective because it uses pre heated case air.
Past that, A AIO radiator complicates creating a positive pressure filtered cooling setup which can keep your parts clean.
And... I have read too many tales of woe when a liquid cooler leaks.
Google for AIO leaks to see what can happen.
While unlikely, leaks do happen.

I would support an AIO cooler primarily in a space restricted case.
If one puts looks over function, that is a personal thing; not for me though.
-----------------------end of rant--------------------------

Your pc will be quieter, more reliable, and will be cooled equally well with a decent air cooler.