The evidence from Mycenaean Linear B suggests that "Potnia" was the name of a goddess (po-ti-ni-ja). In the tablets from Knossos and Pylos her name is often preceded by the name of a place, in the genitive. Its literal meaning is "the Mistress", "Lady".
In re 58: some translators take it as a substantive, others as adverbial. Cunliffe notes that neuter plural [face=SPIonic]nhmerte/a[/face] means "the truth". He also references the construction [face=SPIonic]pa/nta nhmerte/a[/face] in Odyssey 5 meaning "entirely true". So I would vote for "the whole truth". At the very least it's less awkward than construing two adverbials with [face=SPIonic]pa/nta[/face] serving as a substantive, e.g., "quickly and truthfully I will tell you all".