My experience with greenfield is that when you're just starting out, you have to be really strict and careful about overall architecture, establish a framework, provide structure, separate concerns well.

If the project is not throwaway, this first set of iterations is critical, without guidance LLMs will just bolt on things and produce special-cased spaghetti, even the very-frontier models.

Once the framework is established, it's smooth sailing.

But I haven't gotten to "very large" size yet, I expect it produces another kind of coherence problems.