Rent A Room scheme

Hi

Have been looking into HMRC 'rent a room' scheme where one can legitimately take a lodger and earn £4250pa 'tax free' (that is if I've read it correctly).

Having read 'do I need to complete a SA return' I'm fairly certain that one is not required - only other income is from 'PAYE' employment so would just like to check:

1 - Up to £4250 can be earnt 'tax free' by 'renting a room' to a lodger and fulfilling the rules of the HMRC scheme

2 - without having to advise HMRC

Question is would it be prudent to advise HMRC as there are always people out there who think you're doing something you shouldn't & might try to report you

3 - Does using the rent a room scheme have any implications on CGT when selling the house?

Many thanks for all your help and comments.