I would go for something like this:
PCPartPicker part list: https://pcpartpicker.com/list/X2cMnH
Price breakdown by merchant: https://pcpartpicker.com/list/X2cMnH/by_merchant/
CPU: Intel - Core i7-8700K 3.7GHz 6-Core Processor ($369.99 @ Amazon)
CPU Cooler: Corsair - H100i v2 70.7 CFM Liquid...
The Asrock 299 OC-Formula could be your choice, their series always been quite pimped and with plenty of oc options.
https://www.techpowerup.com/reviews/ASRock/X299_OC_Formula/
But maybe too many options if your not hardcore overclocker?
I would personally go with either the Asus Prime or Fatal1ty. They offer great value for the features, perhaps Fatal1ty has better VRMs but if you wont overclock it doesnt really matter.
Had a MSI for my first AM4 and had my fair share of issues, so I wouldnt recommend, maybe was just the early...
I would say, since your doing a unlocked CPU plus the watercooling, get a good overclocking motherboard to go with, get that free extra performance for free. A good motherboard would be either the Z370 Taichi or even the Extreme if you want something cheaper. I'm pretty happy with the Taichi atm.
You can always just got for the GPU upgrade for the time being and later this year, yes we are already in 2018 :D find yourself a new platform, AMD is supposed to release a 12nm Ryzen, might be worth the wait.