Here is the strategy i used:

I had

- 9 Edo Minato frags

- 45 Edo Itachi frags

So i spent ~16k coupons on lucky wheel getting 71 Minato frags + lot of training potions + refine runes boxes

Then i calculated where to spend for Itachi frags (~2 stars per spin in lucky wheel meaning ~300 coupons per Minato frag replacing 1 optional box from fuku or 5+ points per dice roll in lucky board meaning 220- coupons per frag).

I went for lucky board and spent 6k getting exactly 35 missing Itachi frags.

The rest (~3k) i spent on ramens getting ~23 outfit boxes.

In total i got Edo Minato 4 star, Edo Itachi 3 star, about 140 refine runes boxes which enabled me to get the purification pill, around 1400 training potions and other small things resulting in total power increase of ~16k for exactly 25k coupons spent.