If you are going to provide online services then you need to get registered for GST irrespective of your turnover and charge GST and since you are a proprietary concern registered with GST you would also have to charge GST on your offline income even though you have not crossed the limit.
If you take GST registration after it crosses the limit then you need to charge GST only after you are registered with GST.
You just need PAN card and Aadhar card as of now to get GST registration or current bank account in sole proprietorship name.
Yes you can convert sole proprietorship into Pvt ltd company in future.
You just need to maintain all the bills and documents to file income tax return like tuition fees receipt, electricity bill, other bills, bank statement.
If you need any further consultation you can contact me to file your income tax return.
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