I love this thread! Yes, I have dozens of story ideas all at once and scrap books full of stories and plot ideas.
Absolutely!
There are always plot bunnies and random hedgehogs to feed!
To answer your questions…
(1) I try to plot, write, and edit one story at a time, but if I do have a good idea I’ll write it down (and then get back to my planned creative things).
(2) Yes, that “ah-ha!” moment usually comes while writing and after plotting (oh, so that’s how that happens!) or sometimes after the first draft and during editing (oooooh yeah, if I move this here and that there, then it’ll be so much better. Why didn’t I think of that before?)
Glad to see there are other brain full of stories people out there!
This would be my answer, too. 
My head or subconscious is full of stories. I get ideas all the time. Some of the ideas excite me. Others I hardly understand. I write most of them down. I think most ideas can be transformed into a powerful or at least a compelling story. Some take longer to create which isn’t really a bad thing.
Thank You for starting this thread (and to all who have responded in similar vein)! … All this while, here I was thinking I was a lone freak. Why can’t I just focus on one thing at a time? Recently a new writing buddy told me that:
Writing, anything, everyday is great exercise for our writing muscles.
So just do it, she said. —This helped me overcome the ‘Am I haphazard wreck?’ concern. And knowing there’re more of ‘us’ out there further helps to stop stressing over it. So again, thanks.
(1) Do you focus on only one or many stories at a time; on occasion rotating your main focus? - Guilty! It is difficult sometimes to zoom in and out where the works have different themes and tones.
Still, I do it because oftentimes the next part just wants more stewing on (the dough needs proving), wants more of (2) i.e. those ‘a-ha!’ moments still lurking around a corner.
When I’m stuck with one (hating how it sounds, something’s missing, it’s not quite right, etc.) progress at the same time on another project helps keep up the momentum and positivity; and gives me the strength to deal with the issues on the other one/s.
But on the point of working on what appear to be disparate projects, I’ve read as well that the author, Ishiguro Kazuo says of himself that he keeps writing the same book (‘story’) over and over, only in different forms. I take this to mean that he has recurring themes which he conveys in different story plots (and very well).
(2) have you had an ‘ah-ha!’ moment - So wonderful when they happen. Something tells me they don’t occur out of nowhere though.
Happy writing!
Sorry, it would be amiss of me as well, when quoting the Nobel Laureate in Literature, not to mention that he didn’t also drop everything in his day-to-day to complete his winning novel, The Remains of the Day in 4 weeks (working literally, non-stop from 9 AM - past 10PM each day & night). He says of his ‘Crash’ —
'… In this way, so we hoped, I’d not only complete more work quantitively, but reach a mental state in which my fictional world was more real to me than the actual one. . . . This, fundamentally, was how The Remains of the Day was written. Throughout the Crash, I wrote free-hand, not caring about the style or if something I wrote in the afternoon contradicted something I’d established in the story that morning. The priority was simply to get the ideas surfacing and growing. Awful sentences, hideous dialogue, scenes that went nowhere—I let them remain and ploughed on.
—from “How I Wrote The Remains of the Day in Four Weeks,” as published in The Guardian; and
—from Emily Temple’s Nov 8, 2017 piece in LitHub
To paraphrase a saying that was printed on the side of a tote bag that I bought my wife, an avid knitter, “So many story ideas, so little time to write.” The actual saying was “So much yarn, so little time to knit.” As for “ah ha” moments, I’ve had more of them then I can shake a stick at.
OGM! Yes, I’ve so many ideas some are more well-defined than others. Just like you, I read something or hear something, and my mind starts imaging, I just can’t help it.
I am not able to work on several projects at the same time. I get obsessed with the project I’m currently working on I really don’t have the energy to focus on something else.
‘Ah-ha’ moment. Yes, it happens a lot of times. I always feel like a stupid for not having seen it sooner. 
I don’t think I do—it seems I’m always trying to figure out how to get from where I’m at to where I want to go, maybe where that might be. I don’t consider myself a pantser, though, just a plodder. The 'Aha!'s come when one of my choices begins to make sense.
@Danielw I was thinking the passages work sheets are great for folks with all of these ideas at once.
I tend to focus on one project at a time. When I get new ideas, I make a note of them and then go back to the project I’m working on. As to your second question, I do get those moments.
I’m also constantly surprised and (mostly) delighted by the turns my stories take seemingly without my direction!
I have a brain full of stories. I like to have a few projects going at a time. That way, when I get stuck on one project, I just switch to another. Working on another project helps me get unstuck from the first project. I also have numerous notes on story ideas that I try combining in different ways.
Welcome ReLane,
It’s great to have you here!
Have you seen @Danielw worksheet called “Passages” from the PPN+ course?
It works in harmony with what you are describing.
It is so cool that you do this naturally, just BRILLIANT!
I always start out working on a few different projects at the same time but inevitably I’ll get really focused on one project over the others and they’ll fall by the wayside. If I get new ideas I’ll add them to my notes app but I usually end up focusing on the one project until it’s done.
I envy your focus! I am the shiny object queen.
Just say “squirrel!” Hahaha!!!
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A ‘one book challenge’ turned into a series of three, plus a spinoff fourth that might become another series. They are all WIP interleaved at different stages. That’s just the major project. There’s radio scripts and novel outlines been rattling around in my head for 25 years.
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Constantly. Characters arrive in scenes and it’s ‘hello, who are you? What role are you auditioning for? Okay, you’re cast.’
It gets crowded in my head sometimes, like a party full of uninvited but interesting guests. And as I’m writing fantasy, some of them are difficult to throw out.
I bet you get asked a lot,
“Where did you go? You just zoned out on me.” or “You’re not even listening , just staring off into space!”
Folks have no idea that you are listening, it’s simply not to them but the cast performing in your head and THEY are being rudely interrupted!
The struggle is real!
My characters are shy in that they only come out when other (real) people aren’t around. Then they get quite demanding.
Love this thread between @DeAnna and yourself @rtcatling, and I think instigated by our new colleague @ReLane (welcome).
I guess it’s me who is the one who zones out for a while, not just during conversations as something occurs to my characters or in my plot, but for several weeks at a time when ‘real life’ gets in the way.
Inside-my-head-life can be so much more captivating at times. 
When you read back a passage of dialog and find yourself remonstrating with the characters: “can you people try to express yourselves better!?”
That.