GST Registration becomes mandatory once the threshold limit on turnover is crossed. However, in case of export of services GST Registration has to be obtain mandatorily irrespective of the turnover.
Once you obtain your GST Number, you may apply for Letter of Undertaking (LUT) so that you can provide your services without payment of IGST.
Hence, such income from Export of services shall not be taxable under GST. However, the same shall be taxable under Income Tax.
To know more about the taxes exempt under LUT please read: LUT under GST: Making exports without payment of taxes