Obviously AKB48! They're the best group in the world!
hello is better
It's the Cat Empire's 'Hello Hello'.
hello
Yes
No she isn't.
The song is 'Hello' by Cat Empire.
I think pucca is better
hello hello hello
She's not allowed to have a boyfriend because of her contract with hello! project.
beano
You might say "Hello, everyone" out loud, but I would not start a written sentence with it. It's better to be more formal when writing. Of course, if you have a character in a story who is coming into a place and saying "Hello, everyone!" that is different. Also, please notice that there should be a comma between "hello" and "everyone."
She is a member of the female idol group, Berryz Koubou which is under Hello! Project.