I'll answer your questions in the order you asked them. Please feel free to follow up if you would like clarification.
- The universal church is already established. It was established by Christ. Those who believe the Gospel of "The things concerning the Kingdom of God and the name of Jesus Christ" [Acts 8:12] are its members. When Christ comes to establish God's Kingdom, there will be "one Lord and His name one." [Zechariah 14:9].
- Who's the greatest in the world? Jesus Christ. His Father has ordained it to be so. Philippians 2:9. One day he will voluntarily step down from that exalted status when he turns the Kingdom over to His Father at the end of the Millennium. [1 Corinthians 15:28].
- You cannot receive the Grace of God unless you believe that God is and that God can grant you Grace if you follow His will.
Hebrews 11:6 But without faith it is impossible to please him: for he that cometh to God must believe that he is, and that he is a rewarder of them that diligently seek him.
- The memorial name of God is YHWH. The Hebrew alphabet has no letters for vowels so nobody is exactly sure of the correct pronunciation. However, both Jewish and Christian scholars agree that the most likely pronunciation is YAHWEH. The pronunciation of the name is not important. it's what is meant by the name. The meaning enshrined in YHWH is elaborated in Exodus 34:5-7 And the the LORD [YHWH ] descended in the cloud, and stood with him there, and proclaimed the name of the LORD [YHWH ]. And the LORD [YHWH ] passed by before him, and proclaimed, The LORD [YHWH ], The LORD [YHWH ] God [Elohim], merciful and gracious, longsuffering, and abundant in goodness and truth, Keeping mercy for thousands, forgiving iniquity and transgression and sin, and that will by no means clear the guilty; visiting the iniquity of the fathers upon the children, and upon the children’s children, unto the third and to the fourth generation.
That name was enshrined in the "Angel of His presence" in the Old Testament but now that name in all its fullness has been assigned to the Lord Jesus Christ. John 1:14 - see "glory, grace and truth" as an epitome of what was revealed in Exodus. Then see Philippians 2:9-11 Therefore God has highly exalted him and bestowed on him the name that is above every name, so that at the name of Jesus every knee should bow, in heaven and on earth and under the earth, and every tongue confess that Jesus Christ is Lord, to the glory of God the Father. Note he has been given THE NAME which is above every name. It was bestowed upon him as it was on the angel before him in anticipation of his advent. He will surrender that honour when the Millennium is over and the fully completed work of redemption has been accomplished. 1 Corinthians 15:28 When all things are subjected to him, then the Son himself will also be subjected to him who put all things in subjection under him, that God may be all in all.
I hope you have found this helpful.