Why did he attribute the warning not to harm Yakov to "the G-d of your father" and not to the G-d of Yakov himself?
Seforno: Because he did not consider Yakov sufficiently worthy of Hashem appearing to him on his own merit, since he had stolen his heart and fled without informing him.
Why did Lavan add the word "Leimor"?
Oznayim la'Torah: Because Hashem told him to inform Yakov of his dream.
Why is Lavan telling Yakov that Hashem told him not to harm him?
Bechor Shor, Malbim: He shows him that he did foolishly. I have power to harm you. This is why Hashem needed to warn me not to!
Who did Lavan mean that he has power to harm them?
Tosfos ha'Shalem (3, citing R. Efrayim): He could harm Yakov and his slaves. He would not harm his own daughters and grandchildren. Ha'Emek Davar
Hashem told Lavan "Pen Tedaber." Why did Lavan say "Hishamer Lecha mi'Daber"?
Ha'Emek Davar: He lied, to 'prove' that he could ignore Hashem's warning and harm him, just he does not want to. Hashem told me not to speak to you at all, and I am speaking! (Really, Hashem warned him only not to speak bad, but he was permitted to speak good.) I do not fear those who serve your fathers' G-d. I could wipe you out! Amidst my virtue, I request only my gods. He thought that Yakov took them to stop Lavan from idolatry, or to disgrace them. Really, he did fear Hashem's warning. He wanted to uproot everything (like we say in the Hagadah), i.e. to kill Yakov and take his grandchildren, and uproot them from Torah.