Sorry for delayed response.
Answer to Question 1:
I do not believe knowing the author is important. The better question to ask might be: “Where in the word of God is this saying supported?” The answer to that question is the very next verse in Matthew.

Matt 7:24-25 says: Every one therefore that heareth these words of mine, “and” doeth them, shall be likened unto a wise man, who built his house upon the rock: and the rain descended, and the floods came, and the winds blew, and beat upon that house; and if fell not: for it was founded upon the rock. ASV

The “and” is not there by accident. Would it not be biblical to understand that the purpose of “and” is to let the reader know that Jesus has two expectations here, not just one? The first is to “know” his will by going to his word to hear what he has to say. After knowing his will, the wise man is to “do” his will. Knowing clearly come before doing here.

Also consider Eph 6:5-6 which says: “Servants, be obedient unto them that according to the flesh are your masters, with fear and trembling, in singleness of your heart, as unto Christ; not in the way of eyeservice, as men-pleasers; but as servants of Christ, doing the will of God from the heart;” ASV

In this case, would it not be biblical to conclude the heart is the place where we “know” God’s will and would not knowing God’s will come before “doing” God’s will here?

Answer to Question 2:
The meaning of “we need to do God's will before we can become it” can also be seen above in the words of Eph 6:6. Some explanation may be needed to see it.

Consider the wording in 2 Cor 9:7 (Let) each man (do) according as he hath purposed in his heart: not grudgingly, or of necessity: for God loveth a cheerful giver. ASV

Here it is clear that a person can do God’s will with a wrong attitude/heart. This is “doing” without “being”.

Becoming God’s will can also be seen in Rom 12:2 which says:
And be not fashioned according to this world: but be ye transformed by the renewing of your mind, that ye may prove what is the good and acceptable and perfect will of God. ASV

Notice here that “transformation” comes as a result of doing God’s will (i.e. renewing the mind can happen when we use time to hear, read, memorize or meditate on God’s word). Also notice that the “purpose” of transformation is to “prove what God’s will is”. Is this not becoming God’s will?

Lastly, go back to the house that stands in Matt 7 above. There, the result of knowing and doing is standing. Has not that “standing house” become the will of God?

Answer to Question 3: NIV