Hi aswat300,
1. No
2. You would get a valuation done by an estate agent.
3. It is optional
4. There is a possibility but you would need to write in to apply for this and there is no guarantee it would be accepted.
Interest would apply if your payments for the specified dates were late.
5. You can claim for capital expenditure (new bathroom, extension) but not for flooring, carpets,decorating or general maintenance
6. Please see:
CG15250 - Expenditure: incidental costs of acquisition and disposal
Thank you.