How many documents needed to train LLM for an authentic voice?

Hello. In a very specific business niche (boutique consulting firms) I am relatively well known. I’ve written 5 books and perhaps a 100 blog articles.

I would like to use GetCody or similar to fine-tune an LLM on my knowledge, so that my clients can ask a basic question of my data (and the pre-trained LLM) and get a relatively sensible answer.

How much of my content would allow this to work? Thank you!