Hi,
Yes, from next year onwards, you would be required to take gst registration.
Further, sole proprietorship will not help. There is no distinction between sole proprietorship and personal income. If you want to keep this income separate, you need to open a company/LLP.
We arr helping many such clients. Happy to help you.
Further, Why ate you paying 15% advance tax monthly. Advance tax is required to be paid quarterly and after proper calculation.