In my story's lore I've been writing, I've been doing things such as establishing where humans came from and how the new wave of humans understand English and can endure the nuclear environments they're put in, but the worrying at what point can I stop using nuclear mutation to a tool, and to what degree, and have I even been using it enough as a hazard to sell that this really is a nuclear wasteland? What about animals, how will any of them survive, will farmers be paranoid enough to bring their livestock with them into areas of survival or are they just far enough on the edges of the country to establish that they didn't die, leading to farmers going through a sort of, repeat of domestication of irradiated animals and crops? Then I realized after all of this, have I just been over thinking things? Besides, being too thorough leads to potentially larger plot holes opening up, so the biggest question of this all is how far do I have to be thorough to make things believable but not thorough enough I'm leaving every single detail at a risk against me?
A good rule of thumb I heard a while back is to only include details that are either relevant to the plot, or relevant to your characters. Things your readers absolutely have to know so they can fully enjoy your story.
Don't knock yourself too much, It's good that you are thinking about these things. Fleshing out your world is never a bad thing. And doing a bit of research on the subject never hurts (For instance, Chernobyl, the worst nuclear meltdown of all time, hasn't affected wildlife half as much as scientists thought it would. Yes, it has affected it badly to begin with, but if you watch documentaries on the subject, you end up surprised by how much life is there, how some animals have adapated, and how little it affects most animals today.) In the end though, it's a balancing act. In my story, I have an outpost in space. I began writing a few scenes I thought I could do safely, because I roughly knew all I needed. I wrote "the engineer had a team fixing this" and "There were a lot of suspects to go through at the outpost," with that. Then, when I had to go through how my character works out part of the plot, I realized I hadn't taken into account the affect automation would have on this outpost. I delved deeper, and worked it out what jobs the robots did, what would be needed if they broke down etc etc - due to automation and politics, this outpost only had eight people manning it, and it would break one of the themes of my story if it had extraneous people aboard. I looked back at the previous scenes I wrote, and had "engineering teams" that would be one guy at best doing that job. The MC waving to people that wouldn't be there, and would break the plot later down the line. All because I hadn't fleshed out that one location enough in my head. Yep, I totally agree with LastMind, keeping things relevant to the plot/characters is important, Its one of my most important princicples for me, and slowly drip feeding info about your world when an appropriate moment crops up (for me) is the best way of world-building in your books. But, failing to flesh out your world can also have repercussions on parts of your story, if it's involved in the plot. So sometimes we have to do "Behind the Curtain" stuff, so that it makes logical sense to the reader, even if they don't see all of it straight away. I think Brandon Sanderson said in one of his lectures "One guy I know spent six to eight months just creating the world and the plot, because it meant that once he did it, he wrote the book itself in a month and a half, and future books in that series would be quicker to write." If your world is good enough, you don't have to throw it all at the reader at once, or even in the first book (if a series). If they learn a fact in the second book when it naturally crops up, and the world was consistent behind the curtain before that, then they'll go "Ahh, so that made sense back in the previous story, when so n so did X, Y and Z."
Along the lines of everyone else, you need to know the world, the reader doesn't necessarily. If you do the classic, drop the reader in the middle of things and then go on like nothing happened, then the reader will eventually stop worrying about what they don't know. The only caveat is like what they said above: if it's vital information to help the reader understand the story, then yeah, put it in. Man, I feel like an echo... Sorry if this isn't helpful.
As someone who has shallow but widespread general knowledge, I'm often irritated by technical details that aren't right. If the reader is charitable, than yes, they'll accept your mutations for a while, but you're definitely right to limit this. Overthinking is possible and unproductive, but in my opinion underthinking is worse. When I'm at an inpasse, I try thinking of new and creative ways to solve the problem. If you've done your research, you're invincible. The reader probably isn't a radiologist, so you have some leeway with technical mistakes. When it comes to fantastical elements you introduce yourself, own it!
