I joined during the last days of Solano's event, so no kerry till now.
The formation was roughly - archer+soldier to tank first wave into 4 healers+3mages. Every other unit was some sort of tank/soak to be dropped in, other than main tank. I have themis but i found the pure HP of bernice a safer bet over slight MR as my main tank. Soak should have 1.5k hp and above. (conrad, leeanne, rika etc)