1. You can file ITR 4 again because in your above details I dont find any situation which attracts disqualification u/s 44AD(4).
2. ITR 1 and 2 depending on the scenario.
3. Its' like any other business.
4. Books me entry to wese hi hogi jese normally hoti thi. This extension has nothing to do with books of accounts.
5. That depends on what book keeping method you follow. If you follow accrual system show it in march 2020 income if you follow cash system show in april 2020. You can't use mix of both method.
6. Yes. But why would one go to ITR 3?
7. If they are not the actual owner then the right is with your grandfather and you must take his assent to work there.
8. You don't need to show it anywhere. 2 lakh limit for cash gift.
I would suggest you to take phone consultation so that each query can be answered in detail and good discussion can be done.
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Thank you.