Our fears in life hold us back. They prevent us from doing things we want, and they cause our bodies harm with stress. And it's all "in our head". It's well worth it for us to work on those fears, and to move past them. After all, we only have one life - why waste any hour of it in a needless upset state?
I just did a test and it looks like 3,000 words is about four pages of text. In my mind that's a bit short to sell as an ebook. A user might balk at that being "all they got" for their 99 cents (the cheapest you can sell one for).
What I would do is bundle the three same-character ones together as a set. That's now twelve pages which is a good length. It'll have a title page and intro text and then biography at the end, so probably say 16-18 pages in the end. That will be nice. And people will get a "full experience". Start with that and see how it goes. Then you can do a bundle of three related (not necessarily same-character) stories for the next set, and so on. Design the covers and so on so it's clear they're all part of an overall "set" to encourage people to buy them all.
It's fine that they don't share the same characters - my medieval novels are all separate characters. They're all still part of a set.
You definitely want "heading 1" tags for each new story. They're not chapters in a book - but they are each a new heading, with its own table of contents entry.
I'm not sure what the dated concern is. If they're set in the 90s, that is great. People love reading novels set in other times. Just make it clear with some sort of reference, early in the story, when it's set, so they get that sense of place and time.
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