Wideband install

I am wanting to install a wide band with my ebay headers. I am wondering what is the best route to go. Can i just throw the wideband in the post cat o2 sensor and call it a day since my understanding is our post cat sensors do nothing for the car. Or am i mistaken. And how bad is it to miss out on 3 of the cylinders reading. Im doing this because i am planning on doing a turbo build and am going to plan it out like the miata guys do. One small change tune another small change tune....

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Wideband install