The more information I have the better. Do you need to buy an OS? What about monitors?
If you're looking for the best of the best, then you'll actually want TWO PC builds. It's a little bit complicated, but if you want to do it without a capture card, then you can follow this guide.
https://www.youtube.com/watch?v=jROntrxj5-E
This first build would be for gaming. PCPartPicker part list:
https://pcpartpicker.com/list/cVDW9J
Price breakdown by merchant: https://pcpartpicker.com/list/cVDW9J/by_merchant/
CPU: Intel - Core i7-8700K 3.7GHz 6-Core Processor ($347.99 @ SuperBiiz)
CPU Cooler: be quiet! - Dark Rock Pro 4 50.5 CFM CPU Cooler ($84.99 @ SuperBiiz)
Motherboard: Asus - Prime Z370-A ATX LGA1151 Motherboard ($168.96 @ OutletPC)
Memory: G.Skill - Trident Z RGB 16GB (2 x 8GB) DDR4-3000 Memory ($174.99 @ Newegg)
Storage: Samsung - 860 Evo 500GB 2.5" Solid State Drive ($113.88 @ OutletPC)
Storage: Seagate - Barracuda 2TB 3.5" 7200RPM Internal Hard Drive ($58.87 @ OutletPC)
Video Card: Zotac - GeForce GTX 1080 8GB Mini Video Card ($504.98 @ Newegg)
Case: Fractal Design - Meshify C Dark TG ATX Mid Tower Case ($88.99 @ SuperBiiz)
Power Supply: SeaSonic - FOCUS Plus Gold 650W 80+ Gold Certified Fully-Modular ATX Power Supply ($81.99 @ SuperBiiz)
Total: $1625.64
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2018-06-27 12:11 EDT-0400
The second would be for streaming.
PCPartPicker part list:
https://pcpartpicker.com/list/syVphy
Price breakdown by merchant: https://pcpartpicker.com/list/syVphy/by_merchant/
CPU: Intel - Core i5-8600K 3.6GHz 6-Core Processor ($238.99 @ Amazon)
CPU Cooler: CRYORIG - H7 49.0 CFM CPU Cooler ($34.99 @ Amazon)
Motherboard: ASRock - Z370M Pro4 Micro ATX LGA1151 Motherboard ($119.99 @ Amazon)
Memory: Patriot - Signature Line 8GB (2 x 4GB) DDR4-2400 Memory ($78.99 @ Amazon)
Storage: Samsung - 860 Evo 250GB 2.5" Solid State Drive ($79.88 @ OutletPC)
Case: Fractal Design - Define Mini C TG MicroATX Mid Tower Case ($59.99 @ SuperBiiz)
Power Supply: SeaSonic - FOCUS Plus Gold 650W 80+ Gold Certified Fully-Modular ATX Power Supply ($81.99 @ SuperBiiz)
Total: $694.82
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2018-06-27 12:15 EDT-0400
That still leaves you around ~$400 left for a decent monitor. However, there is always the alternative of running on one system. The 2700X is very capable in that use case. I added in some monitors that I think you'd appreciate, though I'm unsure if you'd reach the 144 hz unless you turned off some MSAA or something, which you'd probably do anyway.
PCPartPicker part list:
https://pcpartpicker.com/list/qGnDw6
Price breakdown by merchant: https://pcpartpicker.com/list/qGnDw6/by_merchant/
CPU: AMD - Ryzen 7 2700X 3.7GHz 8-Core Processor ($309.90 @ SuperBiiz)
CPU Cooler: be quiet! - Dark Rock Pro 4 50.5 CFM CPU Cooler ($84.99 @ SuperBiiz)
Motherboard: Asus - Prime X470-Pro ATX AM4 Motherboard ($165.98 @ Newegg)
Memory: G.Skill - Flare X 16GB (2 x 8GB) DDR4-2933 Memory ($225.98 @ Newegg)
Storage: Samsung - 860 Evo 500GB 2.5" Solid State Drive ($113.88 @ OutletPC)
Storage: Seagate - Barracuda 2TB 3.5" 7200RPM Internal Hard Drive ($58.87 @ OutletPC)
Video Card: Zotac - GeForce GTX 1080 8GB Mini Video Card ($504.98 @ Newegg)
Case: Fractal Design - Meshify C Dark TG ATX Mid Tower Case ($88.99 @ SuperBiiz)
Power Supply: SeaSonic - PRIME Ultra Platinum 750W 80+ Platinum Certified Fully-Modular ATX Power Supply ($138.99 @ SuperBiiz)
Monitor: BenQ - GW2765HT 27.0" 2560x1440 60Hz Monitor ($299.00 @ Amazon)
Monitor: Acer - XB271HU bmiprz 27.0" 2560x1440 165Hz Monitor ($599.89 @ OutletPC)
Total: $2591.45
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2018-06-27 12:21 EDT-0400