Answers are as below:
1) Sub-rental income is chargeable under the head Income from Other Sources.
2) Deduction for municipal taxes shall be allowed as it is directly attributable to source of income.
3) You can only claim interest paid on loan taken for construction of property. No standard deduction or principal amount deduction shall be allowed.
4) As a matter of general practice, whatever amount is taxable under the head "income from other sources", any expense which can be directly attributable to the source of income arising, can be claimed and allowed as deduction from that income. However, the same should be in the nature of expense only. Not like payment of principal component of loan or any major repairs or renovation expense carried on the building.
Feel free to revert for any further clarification.