I'm not familiar with your work, skylark, but I wanted to comment on a few things you're saying here.
No, not all fictional characters are self inserts, but yes, a good writer should use their own experiences and (more importantly) observations to breathe life into said characters.
It's not that hard to create a believable character who is not just what YOU would do in a story, nor just the Mary-Sue "Have no fear! I AM HERE! ...WITH MY DEUS EX MACHINA POWERS!".
The character Sajainta mentioned, Wellsville, is goofy, charming, annoying, depressed, bad at what he does, and most of the time very wrong in his assumptions and conclusions. He gets stuck in his own head a lot and has issues he refuses to address and problems controlling himself. Most of the things he does right are by accident. He's not a self-insert, but writing him comes naturally because to me he's almost alive. I'm really proud OF him.
If you have a clear picture in your head about where they came from and what they've been through, make sure your characters have real thoughts and real problems, and you're not afraid to show it on their face rather than have them say it out loud, you can't fail!
Copies of other characters are tricky, because if you do it right, nobody will know it's a copy. If you do it wrong, you're borderline copyright infringement.
Is your work in the Fan Fic section on the Compendium? Or is there some elsewhere I might find? I'd like to take a look-see.