Income from organizing exhibitions

Is your Business  firm /office   location is fix place  or keep changing ?. 

If you exhibition business place  is keep changing no fix place  then  you can  take registration under Casual taxable person , where in you have to deposit  advance   tax  in an equivalent  to the estimated tax liability , please  read  with  section 27 of the CGST act 2017  with rule 15  of the CGST  rule 2017 . I  just  suggest  you ,you can take others opinion  .

well come Sir 

For supply in same state no need to take multiple registrations, only place of supply will change.

for supply in another state other than your registered state then separate registration required, you may register as casual taxable person 

(Note- for supply in same state vertical registrations are possible for different businesses)