I would recommend kaze gaara if you have him since he is a barrier ninja and his barrier raises the ninjutsu and attack of all the earth and wind ninja in your team (specifically him, main and wind blade). The raise is about 40% which is huge.

So your team would be main, iruka, wind blade and gaara.

Onoki is even better for 9 tails if you happen to have him since his barrier boosts wind earth and fire so iruka would have boost from him too.Also he randomly gives an additional standard attack to one of your ninja.
This post was last edited by SenjuMusashi at 2017-5-3 02:06

Formation is the same only with onoki instead of gaara. So ASuma, iruka, onooki and main.
I would put them like this:
Main Iruka X
WB X X
Onoki X X

It also depends what tactic you are using but if you use ghost tactic, then main,WB and onoki will be on ninjutsu boost, which is ok, and iruka on attack boost.
And also, this way, even if you don't use main's clones, only iruka will be hit hard by 9 tails so only he will lose boost from WB, not being at full hp. But even if he does lose hp that will only happen in round 3 or 4 (since he has his own shield which protects him in round 1 and 2), and it's not that big of deal since you are required anyway to RETREAT AFTER THE END OF ROUND 3 cause Onoki's barrier will disappear (so will Gaara's for that matter). And after barrier disappears, THAT's when you really lose damage, and it would be a waste of time to stay another round.
EDIT: Also Onoki or Gaara might lose hp from nine tails, cause sometimes kurama hits all units, and neither Gaara nor Onoki is protected by shields from Iruka. Gaara does indeed give some shields from his barrier passive, however, in practice, they didn't help me very much. Because Gaara either gives shields to only 2 random units, if all are full HP (so he might not shield himself) or to those who lost the most HP (in which case, they already lost their boost from Asuma).
Overall from what I tried, I happened to deal more damage using onoki.

However, I recommend that you try both formations so you see for yourself what's best. :)
This post was last edited by SenjuMusashi at 2017-5-3 16:35

Gaara doesn't always shield himself. It happened to me many times that he shielded others before his first move in round 1 and he then remained open for attack.

Your lineup is pretty interesting.
At first sight, I don't believe it would work better than the one with iruka-wb-kaze, however I could be wrong and it's always good to try new formations cause you might find better solutions that others didn't think of before.
So I recommend you to try what you said at the next 9 tails event and then you can compare the damage and see what formation is best.