Hi welcome to the forum
I would be looking at something along the lines of this:
Cpu - Ryzen R5 1600/X or R7 1700/X if you are doing other things besides gaming i.e Video editing/rendering or twitch streaming etc.
Motherboard - Gigabyte Gaming K5 or 5. These boards support SLI should you wish to add a 2nd gpu later on. You also have Asus, MSI and ASRock X370 boards should you want a different brand.
Ram - A 2 x 8GB 3000MHz kit should do fine.
Gpu - A GTX 1080 ti will give you the best fps at 4K.
Psu - A 750W will allow for a 2nd gpu later. You want a good quality unit such as the SuperFlower Leadex II, Corsair RMx or EVGA G2/G3 etc.
Storage - I would go for a 250GB SSD minimum and also a hard drive for mass storage. If you want to push the boat out on the SSD then look at the Samsung 960 EVO. If you just want a standard SATA then something like the Crucial MX300 is fine.
Cpu Cooler - Some of the Ryzen cpu's come with a stock cooler which is pretty decent (Check listing page). If you want something better then go with either a 240mm/280mm water cooler from the likes of Corsair or NZXT. If you want an air cooler then the Cryorig H7 is a good cheap option. You are also going to need an AM4 bracket. Overclockers stock a lot of them but if they don't have it then you can request it from the manufacturer.
Case - This is personal preference. I like Phanteks, Corsair, NZXT and Fractal Design but obviously choose something you like.
O/S - I assume you are going with Windows 10 ? Get the USB version so that way you don't need a DVD drive.
Mouse/Keyboard - Again this is personal preference. I would look at a few reviews to get a better idea. Even better if you can try them first to get a feel for them.
WiFi - I personally prefer Powerline adapters over pcie wifi cards. They are usually better for online gaming as well and you don't get any signal dropout like you can with WiFi.
