Personality, flaws, etc. What information do you think is necessary for a character profile? In addition, what is some information that isn't necessary but still good to have?
In addition, for things like mannerisms, flaws, stuff in that realm, how many of each do you think is necessary to add, and how many of each more than necessary to have, but still good to have?
Lastly, how much information is too much information? Or is there no such thing?
I think that 'must have' pieces of information are those that are shown in the character's story. For example, if they touch their nose when they're lying. If they do that throughout the story, that's an obvious thing to write in their profile. If they like to put 3 tablespoons sugar into their tea, but they never even get the chance to make tea in their universe, you can leave that information. However, putting information like this one may help to relate to this character more. It's up to you which additional personality traits to write, but the core ones should always be in their profile.
I think that there's no such thing as too much information, unless they don't really match one another. For example, if you write that your character has to plan everything they'll do the next day, they rather won't be open to any sudden changes. Be sure to write info that doesn't contradict itself, and you should be good.
Remember that these pages are mainly for you. You decide what do you want others to know about your characters, and what do you want to know.
Personality and motivation are musts, even if the plot will change the character motivation. I really believe that with those two things, you can tell a story—even if your main character is an incorporeal amnesiac!
What I look for in a good story, though, is the counternarrative: How is your character going to develop? Or, what are recognizable personality traits that might sometimes become flaws in one situation but that are actually superpowers in a different situation of the same story? (This doesn't have to be on the public profile, I'd rather find this out while reading the finished product…but if it helps you get the manuscript written to have this detail written out somewhere and to go back to it on days that you feel lost, then, good! Do that, do what works for you.)
Information that isn't necessary but still good to have…is information that you'll actually use. It's "too much information" if you never use it in the manuscript, or if you use it but it gets in the way of the pacing and plot so your editor says "this scene is better without these paragraphs" and you agree to edit them out. It's good to have if you re-use that unused information for another story.
But I understand not knowing what those specific "nice to have" or "no, that's too much" details are until you're writing things out. There's just that moment when you realize that this scene needs a detail that you can't think up because you didn't think it out. Or the opposite happens, and you realize something like…you've been developing the main imports and exports of your kingdom and the numismatic exchange rates for five years of your life and this story doesn't even have a plot or characters—and the story definitely isn't even about transporting salt herring at two orichalcum ha'pennies worth one copper boggle and a bronze scrabel piece.
Basically, I think there is too much information if you're agonizing for hours and days whether to make one character dishwater-blond or strawberry-blond, when instead you could be writing the dialogue that they have with the person fixing their hair that will get everybody to the next plot point but you're not writing that because you're caught up in the hair or daily/seasonal outfits planning when the story isn't about any of that.
But there isn't enough information if you're not writing at all because you don't know where anything in this scene or setting even goes, so you don't know where to start. If you can't write (especially can't write something that you like) because you don't have enough information about the world, then you probably haven't built enough information about the world.
I read fantasy, and I like reading fantasy, so I'm always up for plenty of detail—architecture, everybody's outfits, landscapes, magic systems, what they're eating, all of it! But I understand that some readers, even some fantasy readers, don't want to read a textbook about the grammar of a language that they're never going to use in real life, or the political geography of a place they're never going to visit, and even I might get bored if I'm told for the fifth time in the same chapter that a character's eyes are violet. So in the latter case, mannerisms might be nice to have and vary it up a bit—but, by no means force it in if your editor says that your character comes off as fidgety and you agree.
Sometimes that "useless" detail needed to be there so you can get the whole thing done the first time, and editing makes it look like you knew what you were doing the whole time (but—shh!—none of us really do!)
Okay, thanks!