Why did Hashem instruct Aharon to strike the water for the first two Makos?
Rashi: Because the water protected Moshe when his mother placed his casket in the river (See Shemos 2:4). Consequently, for him to strike it would have demonstrated a lack of gratitude.
Moshav Zekenim (8:2): Aharon was Moshe's Shali'ach, so he performed Makos from the land. Moshe himself performed what came from above.
What is the last part of the Pasuk ("veha'Basar, Kol Tahor Yochal Basar") coming to teach us?
Rashi #1: It is coming to teach us that not only the owner, but anyone who is Tahor, may eat the Shelamim.
Rashi #2: That although the Basar of a Chatas and an Asham that leave the precincts of the Azarah may not be eaten, 1 the Basar of a Shelamim may be eaten anywhere in Yerushalayim.
Moshav Zekenim: It is put next to Kares for eating Kodshim (the next verse) to teach that one is liable only for what is permitted to Tehorim, but not for meat before Zerikah.