some basic game question

now i am lv 48 with:
stamina 116
atk 116
def 110

how should i distribute my attribute in the future?
i am demon realm so should i focus on atk?

only 3 skills would be active each battle,so does having 5 boost atk/hit def cards unnecessary? is a card like ark dragon which have 17k max atk a better 5th card then a card with 15k atk with boost atk/hit def skill?

thanks