A.) You pray for the forgiveness of your sins because you are commanded to do so. Apparently you missed this verse:
1 Jo 1:9 If we confess our sins, he is faithful and just to forgive us
our sins, and to cleanse us from all unrighteousness.
Confess to who? And why, after we have believed, do we need to confess. John wrote this to believers, those who were already in the Kingdom.
B.) The Blood of Christ is enough. More than enough. But it doesn't work against our free will. We are forgiven when we ask to be forgiven.
C.) We are baptized in water because it is shown in the Bible (Acts 2:38) Water baptism is the covenant ceremony of the New Covenant which has replaced circumcision. Believers are a covenant people, therefore, we follow covenant principles. One of the principles of making a covenant is that there is a ceremony of covenant making. Baptism is part of that ceremony.
D.) Baptism of the Holy Spirit is something different from the covenant making ceremony and baptism in water.
You mistake traditions of man with Holy Tradition. Holy Tradition is that which has been passed down from generation to generation. When the heretic, Arias, was defending his denial of Christ's deity from Scripture alone (sola scriptura) the Fathers of the Church responded with an appeal to Holy Tradition, that is, the way things were always done and always believed.
The greatest example of man made traditions is found in Protestantism, which left the teachings of the Apostles and favored the ideas of mere men who were not taught by the Apostles and did not follow that which was given to the Church in the first century.