You are providing services of online listing. Your customers may be be from multiple states. In this case you will be making interstate supply and limit of 20 lakhs is not applicable to you.
GST registration is compulsory, you have to take registration and charge GST.
Rate for your kind of services is 18%.
Your customers will not hesitate to pay, as they will get input tax credit of this once you file your GSTR-1 return and GSTR-3 return after making payment of tax.