Questions about splitting up my novel

Finish the first draft, or drafts, before you decide. You may come up with more subplots as you go that push the word count up to novel length, or you may find details you can eliminate, making it a more reasonably sized book with three parts.

Also, finishing it with revisions and rewrites, will give you the opportunity to get feedback, see what others like. Publishing companies will probably have their own ideas as well, that's all a long ways off.

The answer is: (hint, it always is) write the book.

Always write the book.

Don't measure your book in pages: what's the word count? And don't fall into the trap of thinking first novels have to be shorter than novels from established writers: that's not true, so long as your writing is tight and clean, and your story is good.

Not at the moment. You find upon revising you'd delete scenes, even entire chapters, add or remove characters, jostle things around, add foreshadowing. Finish the book first.

150 pages is on the short side, but 600 (3x200) feels quite long.

But what everyone else said. Write it and see. Unless you are very disciplined and experienced, books almost never turn out to be the length that you expect. It's probably someone's law. Or if it isn't, it should be. Maybe we could invent a law?

It's a common structural tool for a novel to be split between 3 acts - but neither is a complete story in themselves, but merely show the progression of the story. If you can split your novel into three parts, and each part completes the emotional arc of your protagonist for that section, then perhaps you have three short novels.

If you do split your novel, make sure that the split-off part has a beginning, a middle, and an end: an emotionally-satisfying conclusion.

Can you remind me of the genre, please?

Because for some genres, a length of about 65k is good. For others, it's way too short.

If you have three "acts" each of about 66,000 words that's going to give you a finished length of about 198,000 I think. Which is far too long for any book; and 66,000 (a third, or one act) is too short for the genre you're writing in.

My betting is that you're going to overwrite (most people do), and that you'll be able to prune the book down to a more manageable length once it's done. So write it, revise it, cut it back, and you'll be fine.