1)
Why did he say that he will not eat Mano'ach's bread?
1.
Radak: "Lechem" includes all food.
2)
Why does it say "v'Im Ta'aseh Olah?"?
1.
Radak: If you will prepare the kid for me, I will not eat it. If you will offer it for a Korban, do so for Hashem. In that generation, people offered to idolatry. 1
2.
Refer to 13:16:4:1.
3)
Why does it say "Ki Lo Yada?"?
1.
Radak: This refers back to "Natzerah Na Osach" (we will bring you into our house).
2.
Malbim: Because Mano'ach was unsure if he was a Navi or an angel, the angel did not know whether he offered him to eat, or wanted to offer a Korban.