registration

Sec 22(1) every person liable to register whose aggregate turnover exceeds 20L(10L in scs)

Here as per sec 2(6) aggragate turnover means value of all of outward supply which includes,
Taxable supply
Exempt supply
Export
Interstate supply

And exclude,
SGST
CGST
IGST
UTGST
Compensation cess

So, as per above clarification person falls in compulsory registration.

Yes... As per Query Registration required.

Yes Registration is mandatory