It just seems odd that he needed to sacrifice Prometheans and Humans to make robots. The Forerunners were already capable of making robots.
Perhaps just upload a single Promethean consciousness to a forerunner super computer, right click on the file, click on copy, go to desktop, right click paste. Just copy after copy, ready to be installed on robot units.
Another question, are other forerunners alive aside from Didact? His speech at the end sounds like he's speaking to perhaps a group of forerunners.