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

Source Sheets rebrand.ly/KivreiTzadikim
• 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