1)
Why is he called ha'Erki?
1.
'Rashi': The Targum of "Kiryas Sefer" (Yehoshua 15:15) is Karisa d'Erki (city of Seforim or documents).
2.
'Rashi' citing Midrash Tehilim 3:3: When David sinned with Bas Sheva, he asked Chushai ha'Erki if Hashem will accept his Teshuvah, and give to him Aruchah (a cure) for his sin; he answered, yes.
2)
What is "Re'a ha'Melech"?
1.
'Rashi': It is his close friend. The Targum of "l'Mere'ehu Asher Re'ah Lo" (Shoftim 14:20, regarding Shimshon) is 'Shushvinei'.
