GST clarification for MF distributor

Dear Sir / Madam,

I am MF distributor whose income will exceed 20 lakhs this FY: 2021-22. My questions are as below - could anyone clarify them please? 

1. Will I have to register for GST this FY itself after my income has crossed 20 lakhs (or) if it crosses 20 lakhs this year, then next FY only will I have to register for GST? 
2. When I register & start paying GST, will I be paying personal Income Tax too? In that case, won't the total tax be 18% (GST) + 30% personal tax = 48% total tax?