Lol it's really easy to put a PC together if it's a midi tower or bigger. There's detailed instructions with the mainboard. You can also just ask some nerd you know xD
For $1000 you get pretty highend stuff already.
But be careful that the stuff you buy fits together: the mainboard has to support the RAM and CPU, the GPU needs to be PCIe. Some shops even put the stuff together for you for ~$60.