Rebbe Nachman says in torah 4 of likutei moharan, that in order to attain the level of knowing that everything is for the good, one needs to confess in front of a tzadik, because from there his sins are removed from his bones..
1. Do you know of other sources in the torah where this practice was done?
2. how do we differentiate this, between “talking to the dead”?
3. How often should this practice be done?
Your question is a good one. One of the most difficult pieces of advice to follow is what Rabeinu says and you are referring to that we are to confess our sins before a true torah scholar.
Here is a little background:
Breslover Chassidim were often called Viduinickers because they used to confess before their Rebbe. HOWEVER, Rebbe Nachman stopped this practice and told his Chassidim not to do this anymore towards the end of his lifetime. Rabbi Elimelech of Lizhensk ZT’L writes in Tzetl Koton that one should confess his sins before a true friend which is somewhat similar. However since the time when the Rebbe stopped the practice, Breslov Chassidim confess their sins to God in front of the Tzadik i.e. at his grave site in order to apply this piece of advice. So, no you are not talking to the dead and you should do this as often as you can make it to Uman. This is the simple explanation. I once heard from Rabbi Nissan Dovid Kivak of Jerusalem explain that he understood that confessing in front of the Tzadik is not necessarily literally in front of but in the light of, meaning according to the principles of Chizuk, Good Points etc… that the Rebbe taught us.
Either way stands true.
I know this is still confusing but I hope this helps and perhaps others can fill in some more blanks.