Good advice for starting a light novel?

[Bridge]

For me, the main reason why I try and avoid preparation is because once I have every detail of a story planned, the writing process becomes less about the spark of creativity and more about just copying those details in my head into written prose. It takes a lot of grit and determination to get through it all.

There's no avoiding that. It's busywork, but you just have to try to make it fun I guess. The end result will be so much better if you have it planned out than if you wing it.

EDIT: On the subject of copy-pasting, many of the old masters worked exactly like that. In the field of music, Mozart and Vivaldi for example wrote fully orchestrated compositions in their head before committing them to paper. No doubt there were problems that needed to be solved while doing so, but they had everything planned to the smallest detail so that they had the most control over their work as possible.