Since I do a lot of work in AI and ML (machine learning), most of the stuff I have is geared towards more enterprise applications.

CPU --> i9-9900K

GPU --> RTX 2070 Super (display) & RTX Titan (physX dedicated)

RAM --> GSkill Trident Z 128GB 4000MHz (this is a bit overkill for gaming lol)

For the motherboard, coolers, case, power supply, etc. use what you have and use what works/looks best depending on your setup. I recommend water-cooling the cpu, as well as least an 850W Power Supply if you are going for multiple GPU's.