1. why did he do that? i already know that sory.
2. What Would be the effect on it to naruto?
3. Did itachi Entrust the future of konoha to naruto?
4. Why Itachi didn't kill madara?
1 - To save both Konoha and Sasuke at the same time. To save Konoha without killing Sasuke.
2 - My idea: preventing any uchiha to use the fox without Naruto allowing it. (you know, Sasuke could get into Naruto's inner self and see the fox). To prevent Akatsuki from being able to take the fox out from Naruto.
3 - Somehow. But we cannot be certain if he cared more about Sasuke or about Konoha. He could have also entrusted the future of Sasuke to Naruto.
4 - Itachi was already dying, chances were Madara would win, and if Madara won, Itachi would not have been able to make Sasuke kill him in order to pass his powers over to Sasuke-