http://pcpartpicker.com/list/mKQ9KZ
I downgraded the GPU to a 1060 and kept everything the same.

You don't need to buy a windows license, there are keys for companies called OEM-Keys which are all the same and will always work. Since they are not individual, there have been databanks for a long time.

https://d-fault.nl/Keys Here you can find about 300 OEM-Keys for Windows 7. Just flash an ISO (these 30 day test versions which you can download in many places become "complete versions" after activating a key) onto a USB-Stick or burn it on a DVD.