That's an interesting approach to working with your characters. I never tried that. I see them as people in a little community that interact with each other and the interactions change them as they go.
Pretty much ditto to what has been said. It used to be that people meant something closer to an author's viewpoint or style whn they talked about voice.
But quite naturally, each character has his or her own voice, and that is not the author's.
My characters are all facets of myself, so their voices all have things in common with my voice. However, they're all stronger, braver, better-looking and more interesting than I am, so their voices reflect that. For instance, the protag of my current WIP is pretty tough, having been married to a mafioso's son and run an illegal arms business with him before he got shot down by a bunch of white supremacists. I imagine myself in her shoes, and the voice comes out of that. I think that's why writing her is so much fun. I get to see how I might be in other circumstances. Of course, this is my first novel, so caveat emptor and all that. It may be absolute crap.
This is a great question. Some people would argue that one's character has no voice whatsoever, but is always an extension of the author, regardless of how much distance the author attempts to put between himself and his creation. Once, when asked about whether his characters ever take on a life of their own, Chekhov scoffed and proclaimed: "My characters do what I tell them to."
I think perhaps what happens is an author creates a backstory for a character and attempts to see things from the character's perspective, whether in first or third person, to try and break down the wall between the author and the reader. The flimsier the wall the more immediate the voice and the easier for the reader to connect and be absorbed in the story.
One last thing. In my opinion, the issue of voice should be seamless. Like most elements of fiction, the when the reader is aware of something, such as the use of tense or the structure of plot, then there is something taking them out of the story.
Yes you need to be careful not to interrupt the flow. For me it's as if I'm seeing my character and getting into his head but I guess I'm still doing so using my thoughts and projecting them into the character's situation.
I'm getting better at differentiation voices. I have a background in play writing, so I've put in some time on dialogue, and recently, am able to shift voice in third person POV. I love third person. It's harder to differentiate in first person, for obvious reasons. Viva la difference.