16
Can't even say "git gud". When you play Shuffle you're completely at the mercy of the RNG gods.
One can spend all their amassed stuff for one decisive round, but that's one tough gamble because the game can fuck you over just as well, completely by whim. Just like one, simultaneously, can achieve easy victories (and captures) simply by luck.
There's no other strategy than to spend coins as you deem it viable and brute force, brute force, brute force. Over and over.
You've got fourteen days. Let's say you have three play sessions per day, that's 210 potential victories. Ganbatte.