The Buddha's teaching were first preserved orally by his followers and then later were written down.
Yes, Buddha's first sermon was at Sarnath.
Buddhism is a religion based on teachings attributed to Buddha. Before him, there was no other. By definition a founder cannot be the first follower.
Buddha`s teachings are more important than Buddha himself. Buddha`s teachings are known as Dhamma. Buddha has not appointed any successor after him. At the time of Mahaparinirvana he told to his personal attending desciple Ananda to fallow his teachings after his death.
He strictly followed the teachings of Buddha.
The complete teachings of the Buddha were first written down in Sri Lanka, at Alu Vihare.
We have three books of the teachings of The Buddha, it is called the Tripitaka, literally "three baskets". The first basket is the Sutras, which are the teachings and sermons of The Buddha. The second is Abhidharma, which are philospical discoures on the teachings. The third is Vinaya, which are the rules for monastic life.
Dharma
The teachings of the Buddha
The wheel
Buddha said he was not a God, then after he died people wrote sutras. Many contain things that Buddha never ever taught and so because of false teachings, some people began worshipping Buddha, which they were never supposed to do.
They believe in Lord Buddha. They follow Lord Buddha's teachings.