This is for the singing voice of Nabbit. The same rules apply here as with the normal voice role. You're just singing instead of talking.

I've picked out different lines from certain songs based on the style that best represents the character (The names of each song, along with the artist, will be in parentheses.)

Being an everyman, Nabbit is a guy who only sings on occasions. Be it humming, whistling, or having a part-time job as a barbershop quartet member. When he does sing, I'd like to think he can sing rather well. I don't really have a style for him. Just go with whatever works best. It's probably what he would do.