Something to keep in mind. Green field isn’t always the best answer.
Here’s an example where they took a 10 year old existing application and applied UX. The end user was very satisfied with the outcome, and didn’t care about anything under the covers.
The author came to the realization that doing it this way made the most sense, as it would have taken much longer to start from scratch, and in the user’s eyes would only be marginally better.
Too often we want to re-write a system from scratch rather than update an existing one. Something to be very wary of.