In the New Testament, after Christ is born, he goes about his ministry and gained followers. Though they were not technically known as "Christians" they were called the "Followers of Christ." They became the foundations of would later be branded by men as "Christian."
Personally, I don't know why you say that baptism of repentence is not practiced, because it is the essential part in the conversion to Christ. One is baptized as a symbolic "washing away of sin" which is repentence. Don't get me wrong, I'm not at all saying you have to be baptized every time you sin. It is showing the changing of an old life into a new life with Christ. When baptized, you promise to turn away from your old ways and live a Christ-like life.
Lastly, I personally do not know of any Christian church that claims baptism isn't necessary. If you could please tell me some, that would be much appreciated.
H-D