Mac Pro 1st Gen Graphics Card Question
You should be able to boot without a graphics card, but that will be an easy part to find.  The Wikipedia article is quite good about processor families so you have several options there. The apple power supplies are top notch, but you might find an equivalent. 

Have you considered buying a scrap Mac Pro for it's power supply? I would be hesitant to spend money if I were not sure of the provenance of the stripped Mac Pro you have. (If the Mac worked, why strip the CPU, GPU and power supply? )

Good luck with your frankentosh!