I Have Several Questions About The Rules Of The Death Note.

Hi! I read Death Note quite a while ago, and I unfortunately never took the time to read things like Beyond Birthday. I'm curious about some aspects of the Death Note that I haven't read up on or only think of now with age and hazy nostalgia. Apologies if these questions sound silly, but I'm being genuine with these lines of inquiry.

1.) What makes something someone's name according to the Death Note?

2.) What if someone has a different legal name than the name they identify with? Like, Bruce Wayne is Batman, but he literally perceives himself as Batman, with Bruce Wayne being the costume. If one of his rogues just wrote Batman (and saw enough of his face) would it work?

3.) Do nicknames work? If someone's legal name is "Benjamin," but all their life they've been called "Ben" and identify with the name would it work to write Ben?

4.) If an amnesiac chose a different name as they healed and integrated back into the world, would their new name work? Or would you have to find out their old identity?

5.) Does the name need to be written in the native language of the victim or can it be an approximation of how it would be written in the writer's language? Like if Light wanted to kill the "Hamburglar" could he write "ハンバーグラー," (Hanbāgurā) and it would still count?

6.) Does it work for fictional characters? I know technically characters are just narrative tools with no agency or consciousness, so it's not exactly a life. But could someone write "Bandit Heeler," and Dave McCormack would leave the show? Or would Dave die because he voices Bandit or Joe Brum/Mark Paterson for creating Bandit? Or nothing happens?

7.) If someone's name was written but between the time of writing to the time of the heart attack beginning they finally get the legal name change, would it still work or..?

(Edit: Formatting, on mobile. >n<;;)