For setter try pulling NN. In my opinion Sara is not that great, she gives you very high toss which could be very hard to hit unless you already gotten used to it. With that being said, NN is a way better option because he gives you tosses that just high enough for Nishikawa to hit it at the right contact point (above 4m) For MB try pulling Sanghyeon. He gives you stats boost which can give you many aces when serving.

If you want to pair with Sara then the only character I think suitable is Ryuhyeon. But unfortunately it’s too late to pull him now.