Will his feet actually touch the ground in the second coming?
1 Thess 1:17 states we will be caught up to meet him in the air, Rev 21 seems to support this idea by describing the New Jerusalem coming down from heaven and the bride of Christ (church) is within, and this is after the old heaven and earth had passed away, also backed up in Matt 24:35.
However there are some who suggest Jesus will physically return to Earth. They support this by quoting Zechariah 14:4 which says, "in that day His feet will stand on the Mount of Olives," and Revelation 11:15 which says, 'The kingdoms of this world have become the kingdoms of our Lord and of His Christ, and He shall reign forever and ever!'"
Does Zechariah 14 and Rev 11 describe the second coming?
There is only one future coming of Christ, and when He comes, that is the Millennium.
If there is only one coming of Christ, what is the Rapture?
It is not a coming of Christ to the earth. It is a coming of Christ to the air. Notice 1 Thess. 4:17 says in the clouds and in the air.
Acts 1:9 And after He had said these things, He was lifted up while they were looking on, and a cloud received Him
out of their sight.
The Rapture will take place in the first heaven. It will be instant, in a blink of an eye. No one will see it.
But will He return in the spiritual body He exhibited? Yes (Acts 1:11).
As for Rev. 21, although the Revelation chapters are not always in chronological order, Rev. 21 is a future event, not Christ's coming or the Rapture.
Rev. 21:2-3
2And I saw the holy city, new Jerusalem, coming down out of heaven from God, made ready as a bride adorned for her husband.
3And I heard a loud voice from the throne, saying, "Behold, the tabernacle of God is among men, and He will dwell among them, and they shall be His people, and God Himself will be among them,
2The new Jerusalem is, or includes, God's throne (Rev. 22:1, 3). Heaven in verse 2 refers to the highest heaven.
3God has left the highest heaven and has come down to the third heaven (where the tree of life is).
Rev. 21:2-3
Rev. 22:2
Rev. 22:3
Rev. 2:7, 2 Cor. 12:2, 4