What sort of Ketores did Moshe instruct them to bring?
Ramban #1 (citing Targum Onkelos)
: It was not the Ketores of Mitzvah but frankincense or something similar.
Rashi (on Pasuk 6), Ramban #2 (citing the Tanchuma), Targum Onkelos and Targum Yonasan: It was the morning Ketores of Mitzvah.
In the text of the Ramban, Onkelos translates "Ketores" in this Parshah as "Ketores". In our text however, Onkelos translates it as "Ketores Busmin", which refers to the Ketores of Mitzvah.
Who were the "B'nei Levi"?
Rashi and Ramban: It refers to Korach
and to the remainder of the tribe of Levi, to discourage them from joining him.
Seforno and R. Chananel
: They are the two hundred and fifty men.
Moshe began speaking to Korach softly; but when he saw that he was digging in his heels, he included the rest of the tribe in the warning, before they too, joined the rebellion.
Although Korach argued on behalf of the Bechoros (Refer to 16:1:9:1), that was only a sham