It takes 50 gems to up a 5* once. I spent most of it upping my Kotarou 4* confusion card to lv4 to get max % chance confusion.
I spent about 10 gems upping 2 3* cards to max which were Lucia %hp dmg and Kotori's party damage reduction
I now have like 8 gems and I think 4-5 Mochi.
Yes I got lots of duplicates. But it takes 5 full draws of duplicates to up a 5* once. So yeah I'm not exactly overflowing with riches on upgrade materials.
Oh I guess I should mention I'm a f2p player
So you say some 4*s are better? Would you recommend some? I may not have them though... D: