Besides the "GPT-4 cost about $100 mil to train" number, everything else is still just a number you pulled out of your ass.
Why would you estimate that the $100 million training bill would require a billion in GPUs? That's kind of like saying getting a $100 million of water would take a billion in plumbing.
I don't know what the number is, but I'm not going to start just making them up.