Speaking With a Tzadik at His Kever; a Holy Mitzvah, or a Serious Problem?

Source Sheet (https://rabbikraz.com/TzadikKever) Why did Kalev go to Chevron and not Yehoshua? Is one allowed to visit the Kever of a Tzadik? Is it only to talk to Hashem? May one speak to the deceased? Difference between Tefillah and Techinah? Nusach of a Pa"n