I’ll take these ONE at a time . . .
With regard to Peter being the “Rock” of Matt. 16:18 – I presented a list of respected and eminent PROTESTANT scholarship on the matter.
Protestant Scholars on Matt. 16:16-19
1. There is no distinction between "petros" and "petra."
"In Aramaic 'Peter' and Rock are the same word; in Greek (here), they are cognate terms that were used interchangeably by this period." --Craig S. Keener,The IVP Bible Background Commentary New Testament, (Downer's Grove, IL: Intervarsity Press, 1993), 90.
"Although it is true that petros and petra can mean 'stone' and 'rock' respectively in earlier Greek, the distinction is largely confined to poetry." --Frank E. Gaebelein, ed., The Expositor's Bible Commentary: Volume 8 (Matthew, Mark, Luke), (Grand Rapids, MI: Zondervan, 1984), 368.
"Many insist on the distinction between the two Greek words, thou art Petros and on this petra, holding that if the rock had meant Peter, either petros or petra would have been used both times, and that petros signifies a separate stone or fragment broke off, while petra is the massive rock. But this distinction is almost entirely confined to poetry, the common prose word instead of petros being lithos; nor is the distinction uniformly observed." --John A. Broadus, Commentary on the Gospel of Matthew, (Valley Forge, PA: Judson Press, 1886), 355.
"I grant that in Greek Peter (Petros) and stone (petra) mean the same thing, save that the first word is Attic [from the ancient classical Greek dialect of the Attica region], the second from the common tongue." --John Calvin, Calvin's New Testament Commentaries: The Harmony of the Gospels Matthew, Mark, and Luke, vol. 2, trans. T. H. L. Parker, ed. David W. Torrance and Thomas F. Torrance, (Grand Rapids, MI: Eerdmans, 1972), 188.
"The obvious pun which has made its way into the Gk. text as well suggests a material identity between petra and Petros, the more so as it is impossible to differentiate strictly between the meanings of the two words."--Gerhard Friedrich, ed., and Geoffrey W. Bromley, trans. and ed., Theological Dictionary of the New Testament, vol. VI, (Grand Rapids, MI: Eerdmans, 1968), 98-99.
2. Two different Greek words are used because you can't use a feminine noun for a man's name.
"The Greek makes the distinction between petros and petra simply because it is trying to preserve the pun, and in Greek the feminine petra could not very well serve as a masculine name." --Frank E. Gaebelein, ed., The Expositor's Bible Commentary: Volume 8 (Matthew, Mark, and Luke), (Grand Rapids, MI: Zondervan, 1984), 368.
"When using both the masculine and feminine forms of the word, however, Matthew is not trying to distance Peter, Petros, from 'this rock,' petra. Rather, the evangelist changes the genders simply because Simon, a male, is given a masculine form of the feminine noun for his new name." --James B. Shelton, letter to the authors, 21 October 1994, 1, in Scott Butler, Norman Dehlgren, and Rev. Mr. David Hess, Jesus Peter and the Keys: A Scriptural Handbook on the Papacy, (Goleta, CA: Queenship, 1996), 23.
"The name Peter (not now first given, but prophetically bestowed by our Lord on his first interview with Simon (John 1:42), or Cephas, signifying a rock, the termination being only altered from petra to petros to suit the masculine appellation, denotes the personal position of this Apostle in the building of the Church of Christ." --Henry Alford, The New Testament for English Readers, vol. 1, (Grand Rapids, MI: Baker, 1983), 119.
"The most likely explanation for the change from petros ('Peter') to petra is that petra was the normal word for 'rock.' Because the feminine ending of this noun made it unsuitable as a man's name, however, Simon was not called petra but petros." --Herman N. Ridderbos, Bible Student's Commentary: Matthew, (Grand Rapids, MI: Zondervan, 1987), 303.
"The feminine word for rock, petra, is necessarily changed to the masculine petros (stone) to give a man's name, but the word-play is unmistakable (and in Aramaic would be even more so, as the same form kepha would occur in both places)." --R. T. France, The Gospel According to Matthew, (Grand Rapids, MI: Eerdmans, 1985), 254.
3. "This rock" refers to Peter
"Jesus, then, is promising Peter that he is going to build his church on him! I accept this view." --William Hendriksen, New Testament Commentary: Exposition of the Gospel According to Matthew, (Grand Rapids, MI: Baker, 1973), 647.
"Nowadays a broad consensus has emerged which--in accordance with the words of the text--applies the promise to Peter as a person. On this point liberal (H. J. Holtzmann, E. Schweiger) and conservative (Cullmann, Flew) theologians agree, as well as representatives of Roman Catholic Exegesis." --Gerhard Maier, "The Church in the Gospel of Matthew: hermeneutical Analysis of the Current Debate," trans. Harold H. P. Dressler, in D. A. Carson, ed., Biblical Interpretation and Church Text and Context, (Flemington Markets, NSW: Paternoster Press, 1984), 58.
"By the words 'this rock' Jesus means not himself, nor his teaching, nor God the Father, nor Peter's confession, but Peter himself." --J. Knox Chamblin, "Matthew," in Walter A. Eldwell, ed., Evangelical Commentary on the Bible (Grand Rapids: MI: Baker, 1989), 742.
". . . If, then, Mt. 16:18 forces us to assume a formal and material identity between petra and Petros, this shows how fully the apostolate, and in it to a special degree the position of Peter, belongs to and is essentially enclosed within, the revelation of Christ. Petros himself is this petra, not just his faith or his confession." --Gerhard Friedrich, ed., and Geoffrey W. Bromley, trans. and ed.,Theological Dictionary of the New Testament, vol. VI, (Grand Rapids, MI: Eerdmans, 1968), 98-99.
"The expression 'this rock' almost certainly refers to Peter, following immediately after his name, just as the words following 'the Christ' in vs. 16 applied to Jesus. The play on words in the Greek between Peter's name (Petros) and the word 'rock' (petra) makes sense only if Peter is the rock and if Jesus is about to explain the significance of this identification." --Craig L. Blomberg, The New American Commentary: Matthew, vol. 22, (Nashville: Broadman, 1992), 251-252.
"The foundation of the messianic community will be Peter, the rock, who is recipient of the revelation and maker of the confession (cf. Eph 2:20). The significant leadership role of Peter is a matter of sober history . . . . [T]he plain sense of the whole statement of Jesus would seem to accord best with the view that the rock on which Jesus builds His Church is Peter." --William E. McCumber, "Matthew," in William M. Greathouse and Willard H. Taylor, eds.,Beacon Bible Expositions, vol. 1, (Kansas City, MO: Beacon Hill, 1975), 125.