ashzehedgehog8725-san,
kon'nichiwa.
First about ボク and オレ...
As you know, those two mean "I" and those are "male language". But there're are some (young) girls who want to use
especially ボク to sound a bit like boy or something.
When we female use ボク TO boys (small children), however, it actullay doesn't mean "I". In such cases, we use
ボク to address boys instead (like "you", or "dear").
i.g. ぼく、なんさい? [boku, nansai?] = How old are you?
ぼく、どうしたの? [boku, doushita no?] = What's wrong?/ What's the matter? etc.
In such situations too, we never use おれ to call a boy.
The example you wrote "げんきです。ぼくは?" seems to be the case of this type, meaning "I'm fine, and you?"
Also, the words for "I" should represent "who I am", so as long as speakers say "I", it doesn't matter "to whom"
they talk to. (i.e. It doesn't change depending on the person who you're talking to: boys, men, girls, women, etc.)
I'm not too sure what exactly you want to know in your second question.
If you write a story and give a name of Japan to a character in it, you can decide how this person should be called.
Any of those three should be fine.
Hope this helps!
Natsuko(奈津子),
Team JapanesePod101.com