Buy the fastest non-extreme consumer intel processor, right now thats 6700k, add at least 16gb of ram, 1 mid-size ssd, 2x 4tb drives in raid.
If you want to do any kind of GPU work add the fastest or second fastest consumer nvidia card, like the 1080 or 1070.
If you want to game get a second ssd and install windows on it. It goes without saying one should install some flavor of linux on the first ssd.
This is a sick development machine and represents the sweet spot in price/performance, saving money on your axe is a false economy.
You will also have the ability to overclock in case you come across a task that needs it.