I would focus on power first with coupons unless there is a event with a good ninja in it minato, shisui etc, as for seal scrolls you can get quite a few free a month. 8 from monthly event points 2 from daily sign in if your lucky you can get some from survival trial then there is matsuri and sage battle if you can place high enough. There is also gnw plus most of the time there is a weekly event going on where you can get at least one. Best bet is to save for lucky board you can get quite a few seals if your lucky plus other goodies. Also when you do get scrolls I would save for some kind of rebate to get the most out of your scrolls.