What is the range of aura of a heroe with Aura hability ? One or the number of his magic dice..

This distance is always 1 square. The number after Aura is how much damage it does (ignoring armor)

And your number of magic trait dice has absolutely no effect on any special ability ever printed. It's just used to add dice to magic attacks, peformed Prolonged (Magic) actions in AoD, or when the quest book explicitly tells you to use it.