Kindle Direct Publishing isn't particularly difficult to work with.
Let's suppose you have created an eBook and you've formatted it for the Kindle. Suppose further that you've shown this Kindle-formatted file to a dozen or so advanced readers. Suppose even further that the editor you hired and these advanced readers assure you that the eBook is flawless, perfect, and without any typographical errors, grammatical errors, or spelling errors.
You have to make sure the quality of your eBook is perfect, perfect, perfect, because it bears the stigma of being self-published. Self-published works are looked down upon by many readers. Traditional publishers want everyone to believe "self-published books are trash." They want to serve as gatekeepers. They would like you to believe this is to protect the reading public from a flood of low-quality self-published works.
I wish that were the case. They are simply businesses trying to make the most money they can for their shareholders. They aren't really running a conspiracy to bring in the antichrist or to persecute you. If they believed he could make them a lot of money, they'd publish the devil himself.
- they pursue different markets,
- they already have similar titles for sale,
- they don't publish Commies, Whigs, or Delusional Paranoids.
A thousand self-published works can be great, but all it takes is for the reader to get one low-quality work to vindicate the traditional publishers' propaganda.
Once you upload your eBook to the KDP Bookshelf, there's a chance you'll create that bad impression about self-published work. So, now is a good time for you to ask yourself for the last time why you are self-publishing and also to ask whether you're deluding yourself about your deathless prose.
(You can find the bullet-point outline of How To Publish An Ebook here.)