Hello!

Yes, like what FujiwaraVega said above. 8k Coupons won't gonna get you anything usable at the current metas running around the game. The safe and sure way to get one is to at least collect 25k Coupons and spend it during Fukurokumaru's Deal. Buy the ninja that you need and get free ninja and power items from the rebate. Although most of the commonly used P1 Ninjas these days are worth 28k to 35k Coupons, but by actively participating in every Event of the Cycles, you'll have a chance to get few fragments from Events that gives free points by just doing dailies.

As for the Seal Scrolls, save at least 264 Seal Scrolls and use them during Limited Recruitment so you can get rebates. Great Ninja War Treasure would be the best one to use your Seals.

Thank you.