Here's why you need the training, not the LLM: this is no different than riding a big horse. Data first, talk to the LLM about your data and your users and their needs and what the work you're doing is trying to solve.
Then you start writing spec. The LLM will restart each time, like fucking Groundhog Day. You will have to lead this new instance to your decisions/ and tell it to read everything.
That is the ONLY WAY TO DO THIS.