Gst on commercial property rent income

I own a commercial property which is rented starting from January 2019. Monthly rent as per agreement is 1,90,000 after TDS 1,71,000.

For FY 18-19 no problem as income was for only 3 months. For FY 19-20 i will earn total 22,80,000 which means GST will be applicable as from other thread i understood that beyond 20 Lakh GST is applicable on rental income.

Today i generate invoice without GST. How should i manage this case. I do not have GST registration number. My questions are.

1. What should i do to be ready for Income Tax Filling for FY 19 - 20.

2. Currently i raise invoice without GST amount. From which month i should start raising invoice with GST?

3. What happens to TDS when GST invoice is raised? If someone can share more info about TDS and GST would be helpful.

4. Can i register myself for GST and get registration number or do i have to go through agent or CA?

Any other guidance if some once can share for my case i would really appreciate.

Thanks in advance for your answer.