1. The key word is believe, as in the very next verse that follows it:
"That if you shall confess with your mouth the Lord Jesus, and shall believe in your heart that God has raised him from the dead, you shall be saved. For with the heart man believes unto righteousness; and with the mouth confession is made unto salvation." Romans 10:9-10
What the heart believes the mouth speaks (just like you do here - you express what you believe).
The following is all included in the word
believe that Paul was talking about:
I believe in God, the Father Almighty, the Creator of the heavens and the earth, and in Jesus Christ, His only begotten Son, our Lord, who was conceived by the Holy Spirit, born of the virgin Mary, suffered under Pontius Pilate, was crucified, died, and was buried. He descended into hades. The third day He arose again from the dead. He ascended into heaven, and sits at the right hand of God the Father Almighty, from whence He shall come again to judge both the dead, and those who have been born of, and made alive by the Holy Spirit. I believe in the Holy Spirit, the set-apart-unto-God and universal Christian church, the community of the saints, the forgiveness of sins, the resurrection of the body, and the life everlasting. Amen.
(It's all contained in the Apostle's Creed, which is Christian).
The word believe in Paul's statement does not include your own expressed belief of who or what the Holy Spirit is, nor does it include your own expressed belief that Jesus is not the everlasting God. Nor does it include you expressed belief that God is not a Trinity.
That's because you don't understand your point #1, and you don't understand your point #1 because you don't believe what Paul taught regarding the Holy Spirit, the deity of the everlasting Christ, or anything else that's contained in the Apostle's Creed. You have your own private interpretations of all these things.