How many Buddhas are there?
There had been infinite number of Buddhas before and there will be many more.

In this Kalpa, We already have four Buddhas and there will be one more Buddha. That's why this Kalpa is called Bhadda-kappa.

Extracted it from here.


  In the current kalpa, it is said we are fortunate to have experienced
  five Buddhas. Kusanda Buddha, Konagamana Buddha, Kasyapsa Buddha and
  Buddha Shakyamuni. The Buddha of the future is called Maitreya Buddha.


Read more about Bhadda-kappa from here. At Page 12