So i'm a little confused. AFS NG+ starts from a completed file but do we need to do the extra levels in the bonus world, and do we need to do the boss fights??

The Category "All Front Sides" entitles that all Front Sides of every level must be completed. You do not do anything that doesn't give you an option to do the Front Side of a level, specifically Bosses and Hidden Hills. Rules explain everything, I don't see the confusion.

ohhh ok. Thank you