What is the meaning of the words "Yada Lecht'cha es ha'Modbar ... "?
Seforno: It means that Hashem knew and put into practice that knowledge by providing them with all their needs. 1
Ramban: This refers to Hashem looking after them in the desert, where He provided them with the Manna, the quails and the roving well, and where they lacked nothing that a traveler needs.
As in Sh'mos, 2:25 & 33:12 and in many other places. See Seforno.
What difference does it make whether Hashem blessed you or not?
Rashi: Since Hashem blessed you with all your needs, it would be a lack of Hakaras ha'Tov (gratitude) to behave like poor people who cannot afford to pay for their food and drink. It is therefore correct to buy from Edom, in order to demonstrate your wealth.
Seeing as they were not working, what is "be'Chol Ma'aseh Yadecha" referring to?
What are the implications of "Lo Chasarta Davar"?
Ramban: Refer to 2:7:1:2.
Rashbam: It implies that whatever is unavailable, Hashem gave you free of charge, but wherever something is available, He has given you the means to purchase it.
Seforno: It implies that when Edom comes to sell you food, they will realize it is not because you are short, but to benefit them due to brotherhood, and in order that they will visit you to see the wonders of Hashem.
Hadar Zekenim: You have food and clothing, and the ability to buy, if you want.