If known, have you used the pronouns the individual uses to describe themselves in your story?
This is wrong. An individual doesn't use any pronouns to describe themselves: pronouns are what others use to refer to a third party, usually when they are not present. An individual may prefer, ask or demand others to use specific words to use when referring to them, but no one has any power to compel anyone - nor should they.
If an individual is granted a full GRC they will, from the date of issue, be considered in the eyes of the law to be of their acquired gender.
This is incorrect. The Gender Recognition Act gives a number of exceptions to the holder of a Gender Recognition Certificate being considered as of the 'acquired gender' as specified on her/his Gender Recognition Certificate.
The Equality Act 2010 provides additional exemptions, eg the right to single-sex services.
The Gender Recognition Act 2004 enables transgender people to apply to the Gender Recognition Panel
This presumes a definition of 'transgender', which is a term that is not used or even defined in the Gender Recognition Act 2004.
It would be more accurate to say that the GRA provides a way for anyone who fulfils the criteria in the GRA to obtain a Gender Recognition Certificate.