Why did Pharaoh not ask Moshe and Aharon to leave (as he did above (5:4)?
Ramban (earlier 5:4): This time, when Moshe and Aharon responded to Pharaoh's request for a sign, by proving themselves (at least) on a par with his magicians, their esteem rose in his eyes, and he now considered them equal to his wise men. 1
Moreover, he feared the imminent Makos; and from the moment the Makos began, he became awestricken before Moshe and Aharon (Ramban). See however, Bo 10:28.
Do Kohanim share also in Korbanos other than Menachos?
Ramban: If all the Kohanim share the Minchah, which is of relatively little value, how much more so other Korbanos, which are more valuable.