GST issue in Returns

Mam,  1) What is threshold limit upto which filing of GSTR-9 for FY 18-19 is not required ??

2) What is the last date for filing GSTR-9 for FY 18-19 ?

3) What is threshold limit upto which filing of GSTR-9 for FY 17-18  was not required ??

4) Whether Late fees due to delayed filing of GSTR-1 should be paid through DRC-03 ?

Thanks..