i don't think there's a thing that definitely necessary... it depends on your team...
scenario
1- low dmg? it will be a hell boring long fight, grab few healers to sustain
2- mid dmg? 1 healer is sufficient, put another healer will only get u to low dmg scenario...
3- high dmg? trash mob die in 1 or 2 rounds then Typhoon dies without overdrive goes off, so why a healer? but of course to achieve this u need good hime, eido and weapons..
i got a dark team(all-out offensive) and water team (survival). i would say offensive is fun but bored out of AP....3 hours of AP nature regen and 2 rounds ultimate in 5minutes +- .....