You do what I essentially do. But now that you have all the editing programs, as well as Vellum and extra ISBNs, the cost of doing your new books will be a lot less.

When I pay for a cover, it's usually $150, including the audiobook cover. Since I have a design background, I've recently been using Midjourney and Canva to make my own covers. It's essentially what all the designers are doing these days, anyway. If I can do it myself, why not?

I have 73 novels and 10 box sets on Amazon, published over 13 years, and I have never paid to have someone else do anything except for the covers. Except for the annual costs of the services (Grammarly, Canva, Midjourney and Vellum--all the paid versions), the most it costs me to publish a novel is $150.00. I figure the 'subscriptions' listed above are a cost of doing business, so I don't factor them into the costs for each individual book.

Also, for editing, I edit as I go, plus at the end, I do a thorough read and listen-through using Word's Read Aloud Feature. It does wonders for checking sentence cadence, story flow, and for typos and missed words. You do need to read along as the book is being read to you. But doing this has really cleaned up my books. And then, I run the book through Grammarly, followed by a couple of beta readers who go through the books at the end.

I let Amazon assign me an ISBN for the paperbacks.

As far as copyright goes, it's not necessary to register your work with the Copyright Office. When you create a work, it's automatically copyrighted. But I know people who do what you do, just to be sure. But over 13 years, I haven't had any issues (knock on wood).

I'm glad you've discovered how easy and affordable self-publishing can be. I hear too many horror stories about how expensive it is. (Of course, we haven't talked marketing, which is a whole other subject.).

Good luck ... and now get number three out!