CPU Cooler?

Thanks all for help yesterday! I think I have my compatible parts chosen -

CPU: Intel i5 8600k 3.6GHz 6 Core Motherboard: Asus ROG STRIX Z370-G Gaming LGA1151 (Micro ATX) RAM: Crucial 1x8GB DDR4-2133 SSD: Samsung 850 EVO 250GB GPU: Gigabyte GeForce GTX 1050 2GB OC Case: Fractal R5 PSU: Corsair CSM 550W

2 more bits I need help with- A) Which CPU cooler do I get? Don't really want to get one over £30 or so. B) Would this be able to boot High Sierra? Looked on YT and some videos said to be sure the WiFi's fine (WiFi built into the motherboard).

Edit: Would the 860 EVO 250GB be fine?

Thanks :P