1. As per section 24, Persons who are required to pay tax under reverse charge are liable to take compulsory registration in GST
2. We can't say section 9(4) is suspended as section 9(4) in the year 2017 was deferred for a temporary period and later it was ammended that section 9(4) will be applicable only for supply of SPECIFIED category of goods or services or both to SPECIFIED CLASS OF REGISTERED PERSONS. The specified goods and services and persons are notified in the notification 07/2019 CT(R) dt 29/03/2019