I think your uncertainty around your own choices is really holding you back, especially considering how many threads you've made
No-one is gonna know your story or your vision as well as you are- we can give you critique on how to convey your intent to readers in a comprehensive way, but at the end of the day, you're the one who has to sit down and figure out what to do with the story.
The answer to most of your questions would be: If you want to. If you feel it would improve the story. And honestly, you won't always know! Writing is often problem solving, and a clear vision for your work may not be apparent until you've done a ton of work for it.
Based on my own experiences writing, changes later on are inevitable. I find that with everything I write, the first scene is re-written at least 3 times after I work out what happens very late into the story. How I got to that point was not asking people what i should do- but just writing the story, going back and editing and adding and completely axing scenes because I now have a further understanding of my story. And that understanding will not come if you're just focused on ideas and not execution.
Just write. There will never be a time you won't be uncertain about your choices, but save your old story versions and writing in case you want to come back to it. Just go for what you're considering if you think it's right for your work, and if you're wanting to grow an audience: try to write with people who don't know your world and characters in mind.