Anyone kindly share their real life self publishing experiences?

For a writer and a human being known infamously as a rather verbose man who can’t stop talking or indeed writing, this will be, for me, a very brief article and indeed a shout for help into void of The Matrix.
Kindly David Perlmutter has sincerely piqued my interest in self publishing my first book and I’ve no doubt that David will come riding to the rescue once more to answer the following questions. Because he’s a kindly Canadian and so much more! But for first time readers of mine, it’s a long story which I’ll condense thus:
I’ve written a book which will be ready for publication on or just after 28th May. It’s an opus piece of writing, a passion project, a calling, a purpose and a raison d’être if you will. My heart and soul is in this damn book!
I’ve sent numerous emails to publishers who have either (a) ignored me (b) quoted me ridiculous prices or (c) ignored me. I have no Agent. No submissions from new writers without an Agent. Blah boring Blah.
I have an “in” with a possible publisher but hold out little hope and anyway, following David’s suggestion, I’m SERIOUSLY on the brink of using Amazon KDP.
I could obviously get the answers to these questions via Youtube videos etc and I have, kind of. But I’m looking for a human being and genuine human reactions as to your experience(s) of publishing on this platform. So:
Do you have to transfer the entire book, as is, or can you edit within the Amazon programme?
Same goes for the cover? Can you edit or do you have transfer as is?
I’m largely using my own pictures from my own private collection but can you use images from the internet if you duly note the website/copyright holder?
What are you PERSONAL experiences of using the self publishing tool?
Is it straight forward for someone, like myself, with only a rudimentary knowledge of editing/transferring?
I also don’t have “Word”. Will this be a problem?
I probably have more questions but this is a quick, on the hoof article as I’m so keen to get going (as is my way) but equally I don’t want to set myself up for a huge fall and obvious disappointment as this truly is my motivation and that beautiful phrase, my raison d’être.
I’d say no spammers or leaches or people seeking a quick buck at my expense but alas such is life and such is The Matrix!
Over to you David! And of course anyone else who reads this and has a genuine, human reaction to their experiences of self publishing.
Thank you for reading. Three recent articles of mine should you desire some football writing, a spoiler free film review or some images full of April sunshine from the UK:
Salah and Jota cut down Forest
Liverpool 3 Nottingham Forest 2, 22nd April 2023.medium.com
“JoJo Rabbit” (2019)
Highly recommended satirical comedy.medium.com
Beautiful Gnosall in the Spring sunshine
“These are a few of my favourite things”.medium.com