Saving is the smartest thing to do, in my opinion.

Just be sure to not let power get in the way of fun!

This event there is lucky board so your priority in coupons spending is there, since for a new player is really a ton of power.

spend everything on lucky board

Save your coupons and spend it on something that can increase your power or you'll be sorry if someone beat your as* in some events and leave you crying. (refines and other upgrades is what im talking about btw)

Off the bat, Stack coups, save them for lucky board. Once you notice that your power is no longer increasing through the board, just spend into other events like treasure of the sage with big discounts on power items. Ideally in the board you want to stack Medium refines and Charms. Although, CHarms may be the best value from the board since you can stack refines through the monthly event now. NEVER EVER BUY ANYTHING FROM THE SHOP! Only unless you see a good value in the "purchase limit" section of it. Mags will be handed to you over time through practically everything.

I spend the first few coupons to get GNW TenTen and/or Iruka fast then save the rest for Lucky Board. It's really worth it.

Iruka fast is a good idea as he will help you to get possibly top 3 in 9 tails so you can get even more coupons. In a sense he pays for himself over the long run.

After that, just like everyone says spend on lucky board only and you will win this game.

Tips:

Save coupons wait for rebates.

If you have the urge to spend them-lucky board(why gives power items)

Spend on power especially if you are f2p or a casual spender.

Save seals for rebate.