I want to become a singer, so what should I learn Hindustani classical or light vocal?

Vocal classical music will help you to sing  not only light classical but also all type of song. Voice culture will help you to improve your vocal. Learning vocal classical you can understand about voice modulation which is very important for light music. And also you can learn about breathing techniques which is very helpful for any kind of music

what kind of singer Professional or Ameture ( for example to satisfy your hobby in singing). For Profesional or ameture singing, you will have to train your voice by learning hindusthani classical music at lest for 2 to 3 years atleast to master the nuances of classical music.

To be a Professional singer it is entirely your luck, contacts & your base of singinging. Even the champions of SAREGAMA competion have been forgotten after the competition. 

Thanks & Regards