Hi,
Thank you for your questions.
A) I would refer you to:
Abolition of the furnished holiday lettings tax regime - in particular the section headed 'Proposed revisions' which details the use of BADR and the time frames.
B) As regards the cessation of the FHL, you need to tick the box on the SA105 page when you complete your self-assessment tax return.
C) If you are ceasing the FHL because it does not meet the availability criteria, any income received from the property after that date will be just normal rental income and should be declared as such.
You may also be interested in looking at:
CG73500 - Furnished holiday lettings: general which is information on FHL's and Capital Gains and also:
CG63965 - Business Asset Disposal Relief: meaning of business which gives more information on BADR and what is classed as a business.
Thank you.