What is "v'es Aharon v'es Banav Tifkod" referring to?
Rashi and Rashbam: It refers to the appointment of the Kohanim - to the Avodos of the Kohanim, 1 as the Pasuk goes on to explains.
Rashbam: It refers to the appointment of Aharon and his sons over the Levi'im.
Rashi: Kabalas Damim, Zerikah, Haktarah and the other Avodos that are confined to the Kohanim.
What is "v'Shamru es Kehunasam" referring to?
Rashi: Refer to 3:10:1:1*.
Seforno: It refers to the Kohanim guarding the areas from the Mizbe'ach and inwards, as well as inside the Paroches, to prevent the Levi'im from entering.
And finally, what is "v'ha'Zar ha'Kareiv Yumas referring to"?
Seforno: It is referring to a Zar who comes to perform the Avodah of a Levi or of a Kohen?