1) Why would asking God for food have been bad In response to Satan’s suggestion? Jesus replies, “It is written: Man does not live on bread alone, but on EVERY Word that proceeds from The mouth of God.” (a reference to Deuteronomy 8:3)
Yes, Jesus would have been famished! There are other cases in The Word of prolonged (40 day fasts) Moses, Elijah, Joshua were precursors. https://pin.it/2NgKOqD
It touches on the literal bound of survival.
Jesus Knew The Word intimately.
He IS The Word made flesh. (A concept difficult to understand I realize that. But, this is explained by Jesus’ impressing the elders in the synagogue at age 12. Luke 2:41-52 https://www.google.com/amp/s/www.biblegateway.com/passage/%3fsearch=Luke%2b2:41-52&version=NIV&interface=amp
Yes, He had to read/learn/practice Who and What He IS.
To focus though on the question about a 40 day fast, Why? There were previous accounts of what had been done. Jesus was led into the wilderness by The Spirit. He was sent for a reason; He knew this intimately BECAUSE it is mentioned several times in the Old Testament:
Old Testament prophecy about Jesus’ death fulfilled
Crucifixion by death was for murderers and thieves; but for a Jewish man named Jesus, who claimed to be the Messiah, it was the ultimate sacrifice.
Jesus’ death was prophesied in the Old Testament hundreds of years before He was crucified. When the Roman soldiers took Jesus before Pilate, the disciples already had abandoned Jesus.
Zechariah 13:7 is the scripture Jesus quoted: “God will strike the shepherd and his sheep will scatter.” Isaiah 53:7b says, “He was led like a lamb to the slaughter and as a sheep is silent before shearers, He never said a word.” Psalm 22:16 states, “My enemies surround me like a pack of dogs; an evil gang closes in on me. They have pierced my hands and feet.”
This scripture was written by King David in approximately 900 B.C.; crucifixion had not yet even been invented. Jesus was beaten with a lead-tipped whip that ripped His flesh from his back. Isaiah 50:6 says, “I offered my back to those who beat me and my cheeks to those who pulled out my beard. I did not hide my face from mockery and spitting.” Psalm 22:14a, 15: “My life is poured out of me like water, and all my bones are out of joint. My strength has dried up like sun-baked clay, My tongue sticks to the roof of My mouth. Psalm 69:21b: “They offer me sour wine for my thirst.”
The soldier offered Jesus wine mixed with gall, rather than water for His thirst. Psalm 22:7-8a: “Everyone who sees me mocks me, they sneer and shake their heads saying, Is this the One who relies on God? Then let the Lord save Him!”
This was when Jesus – The Word of God made Man came as a result of a challenge made to God