1. You do not need to register under GST if your total receipts during the f.y.are upto 20 lacs.You do not need to register under GST even if your total receipts are exceeding 20 lacs but you are providing services exclusively to your foreign clients and receiving money in convertible foreign exchange.
2. If your total receipts during the f.y. were exceeding 20 lacs and you were not providing services exclusively to your foreign clients then you need to take GST registration and pay GST along with interest and face other consequences.
3. Although compliances of GST and Income Tax are totally indifferent and you need not to take GST registration to file Income Tax return but income generated under both can be crosschecked by the authorities.Like when you will show your source of income and total income generated in your income tax return, authorities of gst might fetch that data from income tax department and may ask you to justify why did you not get registered under GST and paid tax.
So before taking any step further you must consult some professional and let him deal with it.