How to proceed with gst (web developer)

I am a webdesigner. Registered as proprietor in Punjab.
The work is done occassionaly, and most of the time done online, for people / firms in some other state.

How should I proceed with GST. Should I register directly under GST?? , or register as Casual Taxable Person??
If as casual taxable person, what values whould I fill in turnover and tax liability  (Integrated tax , central tax, state  / ut tax, cess)

Is it necessary to register under gst before registering as casual taxable person??
The amount is in few thousands, and done occassionaly, but all companies now require to tell the GST number.