Yes that is basic ! Jesus stated who the all are He died for here Jn. 10
Nope
Sheep is not a synonym for world , all men, all etc
John 6:51 (KJV 1900)
51 I am the living bread which came down from heaven: if any man eat of this bread, he shall live for ever: and the bread that I will give is my flesh, which I will give for the life of the world.
Hebrews 2:9 (KJV 1900)
9 But we see Jesus, who was made a little lower than the angels for the suffering of death, crowned with glory and honour; that he by the grace of God should taste death for every man.
2 Corinthians 5:14–15 (KJV 1900)
14 For the love of Christ constraineth us; because we thus judge, that if one died for all, then were all dead: 15 And that he died for all, that they which live should not henceforth live unto themselves, but unto him which died for them, and rose again.
1 Timothy 2:4–6 (KJV 1900)
4 Who will have all men to be saved, and to come unto the knowledge of the truth. 5 For there is one God, and one mediator between God and men, the man Christ Jesus; 6 Who gave himself a ransom for all, to be testified in due time.
John 11:51 (KJV 1900)
51 And this spake he not of himself: but being high priest that year, he prophesied that Jesus should die for that nation;
and sheep are followers
John 10:4 —KJV
“And when he putteth forth his own sheep, he goeth before them, and the sheep follow him: for they know his voice.”
John 10:14 —KJV
“I am the good shepherd, and know my sheep, and am known of mine.”