If I may be a little harsh for a moment...

Gaara's and Sasori's mysteries are both ninjutsu based, meaning to say Poison Tai wouldn't help them at all.

Sasori's standard attack with puppet already has poison, so that's another redundancy for Poison Tai.

Sasori's mystery is non-prompt, so I wouldn't count on it being first slot as my combo trigger.

Now if I were to put my touch on this team, it would go something like this:

Water, Gaara, Blank

Tsunade, Sasori, Blank

Blank, Blank, Blank

Talents would be 2 2 2 2 1 Shiba or 2 2 3 2 1 Monkey. The Shiba talents allows me to move Tsunade down 1 grid so that she can share the heat with Sasori if there's an enemy at the bottom row. But if Sasori is disabled, my entire combo chain dies, which is why I thought of the Monkey talents.

So now, the whole idea is that round 1, Gaara breaks auto barriers, while Sasori acts like *l-round tougher version of Kankuro (i.e. 100% combo starter). Round 2, If Sasori c*e his mystery, then great. But most times, I'll be using Water's Great Shark Bomb instead. Round 3 will be either Gaara's mystery or Tsunade + whichever is left between Iron Sand World Order and Great Shark Bomb. From here, I'll try to make sure that every round, I have either Gaara's mystery part 2, Water's mystery or Sasori's mystery to AoE with, even if it means that I have to refrain from throwing out all my available mysteries despite my abundance of chakra.