Nil return

yes. need to file the nil return

u have to filed gstr3b nd gstr1 for the month of march as nil... 3B late fee per day 50 (last date was 20th april) they will charge this late fees in next month 3b. nd gstr1 last date if u opted for quarterly then 30 april nd if monthly then 10 may, but u can filed this retrun ,they are not charging late fees for gstr1 now...

You need to file both GSTR 3B and GSTR 1. Filing of GSTR 3B is very simple as you will asked whether you like to file nil return. For GSTR 1 prepare it online, just enter turnover details as asked, generate summary and file. 

Yes, GST returns are required to be filed, even nil returns. For Nil Return- 3B, (At present) Penalty is Rs. 20 per day

Yes you are required to file a Nil return.