Who was the "Ish" who found him wandering around in the field?
Rashi and Targum Yonasan: It was the angel Gavriel. 1
Hadar Zekeinim and Rosh: "Ish" is the Gematriya of Refa'el.
Rashi says that the "Ish" was an angel. Why did Hashem send an angel to lead him to his brothers? Why would it not have sufficed for the Midyanim to have found him and sold him to Potifar directly?
Oznayim la'Torah: The time had come for first Yosef, 1 and then Yisrael, to go down to Egypt, and lest anyone think for one moment that the events that now unfolded were natural, Hashem first put it into the head of Yakov to send his favorite son to his brothers, whom he knew, hated him, and then an angel to assist him in finding them, to make it abundantly clear that it was all min ha'Shamayim (since it was all part of His Divine Plan).
Oznayim la'Torah: Had the Midyanim found Yosef and sold him to Potifera directly, people would have wondered, when his father and brothers followed, what Yisrael had done wrong to be subjugated and enslaved more than any other nation. 2
What is the significance of the phrase that Yosef "was wandering around... "?
Ramban #1 and Rashbam: This teaches us Yosef''s Tzidkus - despite his brother's hatred, he refused to return to his father without having fulfilled his mission.
Ramban #2: Moreover, it teaches us that when Hashem issues a decree, nothing can prevent its fulfillment. Having decreed that the Galus was due to begin, 1 when Yosef could not find his brothers (who were destined to set the Galus in motion), Hashem sent an angelic guide to lead him to them.
Da'as Zekeinim: The word "To'eh", and also "va'Echar Ad Atah" (Bereishis 32:5) hints at the three Galuyos - 400 years of Galus Mitzrayim ('Tav'), 70 years of Galus Bavel ('Ayin') and Galus Edom, which will end after the year 5000 ('Hei'). 2
Why does it say "ba'Sadeh" (which implies a known field)?
Malbim: This is the field that Yakov bought from Bnei Chamor. He thought to find them there.
If the "Ish" was a stranger to Yosef, why did it suffice for Yosef to say "my brothers"? And why did Yosef expect him to know where they are?
Ha'Emek Davar #1: Yosef was known to them to be important (so they would know also his brothers).
Ha'Emek Davar #2: Yosef recognized that he is an angel or Navi.
Ohr ha'Chayim (16): "Leimor Mah Tevakesh" (verse 15) implies that he asks him what he seeks. 4. Malbim (16): Usually, shepherds go from pasture to pasture. They do not go far away.