What I have automated is actually to find good chunks (in this order: heading, paragraph, sentence, word, non-alphanumeric, mid-word), feed it to gpt-35 (cheap,

What I have automated is actually to find good chunks (in this order: heading, paragraph, sentence, word, non-alphanumeric, mid-word), feed it to gpt-35 (cheap, fast) and give it the previous chunk summaries up front telling it to leverage the context, but not include them in the next chunk summary. Finally, when I have all the chunk summaries, I feed them to gpt-4 for aggregation ("smarter"), telling it not to shorten the overall amount of text. Works decently well.