1)
Why was it necessary to assemble all the people and for them to lean their hands on the Levi'im?
1.
Rashi: Since the Levi'im were being given as a Korban Kaparah instead of them, it was fitting for them to stand by their Korban and to lean their hands on it.
QUESTIONS ON RASHI
2)
Rashi writes that Moshe assembled all the people to stand by their Korban, since the Levi'im were given as a Korban in their place. But they were only in place of the Bechoros?