I would like to sell my CUSTOM word search books on Amazon.

My ideal scenario would be ONE listing where the buyer can either choose a predesigned book or customize and order the book.

From what I understand, I can not use KDP to do this because KDP listings can not be customizable.

1. Is there a way to use only KDP? I would like to use KDP because it would avoid the $0.99 fee for every item sold through an individual seller account.
2. If I can't use only KDP, can I use KDP to print and fulfill the predesigned books and another service (like IngramSpark) to print and fulfill the custom books from 1 listing? To put it another way, can I publish the predesigned books through KDP and link to them as predesigned options in the custom listing? That way I avoid the $0.99 fee for the predesigned books and only pay for the custom books.
3. Will I have to use KDP for the predesigned books and my seller account for the custom. This means I would have multiple listings, one for the custom book and one for each predesigned book. This is not ideal.
4. Should I just forget KDP and go with the third party POD service?

Please tell me where I am wrong and what you would do. Thanks.