Why was Aharon instructed to perform the plague of lice and not Moshe?
Rashi and Targum Yonasan: Because it entailed striking the ground, which would have demonstrated a lack of gratitude bearing in mind that the earth protected him when he buried the Egyptian in the sand. 1
See Sh'mos, 2:12.
Why did Hashem not warn Par'oh about the plagues of lice, boils and darkness?
Ramban (on Pasuk 15): He only warned Par'oh before the Makos that resulted in human death or destruction. 1
Rashbam and Seforno: Refer to 7:26:1:2**.
See Ramban DH 'u'Mah she'Amar'.
What is the significance of the fact that Aharon struck the water (See 7:20) and the earth?
Oznayim la'Torah: Because the Egyptians forced Yisrael to make mortar and bricks out of earth and water, Hashem brought on them the first group of Makos by striking the earth and he water.
What was the significance of 'D'tzach' (the first set of plagues) that ended with Kinim?
OznayIm la'Torah (citing Abarbanel): It was to teach Par'oh that Hashem exists 1
Why does the Torah talk about the Kinim as if they also came in Eretz Goshen and as if they affected Yisrael as well?