Well, a story is not their premise. Whether you have more or not, I can only judge by what is there. As a story is the sum of its parts, leaving out critical details means you leaving the puzzle half finished. I know you wouldn't want to reveal your entire story, but it just works that way. Additionally, if your character's personalities can't be fleshed out and described without spoiling your plot, then that may be a sign of the problem I was talking about that can risk the quality of your characterizations.
Project 1: If I were to make a suggestion, I would delve down deep into what the point of the story is. Not in the plot, but thematically. Characterization and character arcs are defined by themes. Or, at the very least, they should be. It provides a more coherent narrative that way.
Project 2: Personally, I would suggest starting over and simply reusing ideas if they work. You don't have to salvage every idea.
Project 3: I understand that. I figured it was something like that from the first two character description. Mind you, having that sort of theme is a good thing. I forget if I said it, but as of now, with what I know, they feel like a good example of characters created to serve a plot than to be characters themselves.
I guess the question that you should ask yourself is this, "Is this character like this so the plot advances how I want, or are they a fully fleshed out character who make all the choices set out by the plot?" Subtle difference, but it depends on how you treat the character too. If you're just thinking of characters to serve your plot, then they will end up being a plot point to both you and the audience. You'll end up treating your characters like that as well, even if just out of habit. Again, this is based on what I've been provided.
Personally, when I think up stories, its a two branched method. On one side, I decide the theme. The point of the story. From that, you can get the groundwork of your characters. On the other side, you have your basic premise, and the premise decides the world. It fleshes it out and creates something the characters could actually live in. When you combine these two paths, the story begins to tell itself. Now, I'm not telling you that you have to write this way, or even that you don't understand this already. I'm just explaining where I'm coming from. Its important the story comes naturally from the characters. Otherwise, you risk forcing the plot or inconsistent character personalities.
As for your last question, I was more referring to world building. Magic item stories are mostly distinguished by their world building. With appropriate lore surrounding it, the stylization that can make each aspect of the plot and visuals unique start to form.
Project 4: I was mostly trying to emphasize that interesting characters are the crux of such an idea (and that sci-fi usually has a hint of mystery, but that's for another day). So, its important to spend most of your time molding the characters' personalities and, more importantly, the character interactions to be unique, natural, and interesting.
Project 5: Yeah, all I'm basically saying is to flesh out to make it more complicated. As of now, it doesn't sound interesting enough to go beyond the cliche. A variety of ways this can be done. One idea that comes to mind is to establish a more complex set of rules for how the alternate personality works. If you have a rulebook in front of you, then its easier to write the mystery side to it.
Project 6: Sort of like Project 5, there just isn't enough to it for it go beyond the cliche at the moment.
Its also worth to note that I don't like premises that are designed to last a long time. I'm a firm believer of a story being made with a beginning, middle, and end. So ideas like your artifact one, which strike me as an 'artifact-of-the-week' style story than a premise with character arcs and a plotline. Sure, there can be an overall plotline, but it feels like you're focusing more on the what would be done on a chapter basis than what the end goal of the story is.