What exactly was Yosef telling his brothers, that they did not already know?
Ramban: He was telling them that they had no reason to be upset at what they had done, because it was an act of Divine Providence, inasmuch as due to the two years of famine that had already passed, grain was so scarce and expensive that, if not for the fact that (thanks to their efforts), Yosef was in the position that he was, they would never survive the five years of famine that were still to come. 1
He did not know, of course, that the famine would cease with the advent of his father, but then that too, only occurred because he was there. (EC)
Why did Yosef say "v'Atah"? And why did he say "Al Te'atzevu" and "Al Yichar"? They are opposites! Sadness is from a broken heart, and anger comes from haughtiness!
Ohr ha'Chayim: I know that you regret the sale. They said "Aval Ashemim Anachnu" (42:21). Bereishis Rabah (91:6) says that they descended to redeem him for a great price. Yosef said, now that you achieved your goal, do not be sad. This also showed that he knows that they feel affinity for him, and it is proper that his heart is Shalem with them. Do not be angry that your sale led to bowing to me, the opposite of your intent ("let us see what will be [of his dreams]" - 37:20). One who comes to fix a matter, and he ruins it, he gets angry. Just the contrary, "Hashem sent me for sustenance!"
Malbim: If you are sad amidst regret of your evil deed, or angry that you sold me "Henah" (where I rose to greatness, and not elsewhere). Do not think that I will do evil to you. "Hashem sent me for sustenance in front of you," and not for evil!
Ha'amek Davar: One who falls in his own eyes, he is sad. Anger is when another harms him. Some brothers regretted their evil deed, and others still thought that it was proper to sell him, just it was foolish to sell him to Egypt, where it is possible to rise to such greatness; 1 they should have sold him to a minor country! Both of these are improper thoughts. It was Hashgachah that you sell me to Egypt, for sustenance!
Ha'amek Davar: Surely awesome Hashgachah was needed to turn a slave into the ruler. Hashem could have done so also had they sold him to a minor country! Also, they should infer from the Hashgachah that the entire sale was a mistake! (PF)
Why does it say "Yichar b'Eineichem"? Usually Yichar is followed by a Lamed (e.g. Lo, Lecha, l'David...)!
Ha'amek Davar: Yosef knew that now, they did not regret that he is alive. They came to redeem him (Bereishis Rabah 91:6)! However, perhaps they are pained b'Eineihem, i.e. their intellect is pained that they were foolish before.
QUESTIONS ON RASHI
Rashi writes: "For sustenance - [I.e.] for your sustenance." What is Rashi clarifying?
Gur Aryeh: Do not interpret that Yosef meant, that Hashem had sent Yosef ahead to ensure Yosef's own sustenance; but rather, to ensure that all of the brothers would live.
