Monarch displayed in museum – initially housed show in ground-floor extensions (9)

'monarch displayed' is the definition.
I can't judge whether this definition defines the answer.

'museum initially housed show in ground-floor extensions' is the wordplay.
'museum' becomes 'V and A' (Victoria and Albert Museum).
'initially' indicates taking the first letters.
'show' becomes 'ER' (US medical drama).
'in' is an insertion indicator.
'ground floor extensions' becomes 's' (I can't explain this - if you can you should believe this answer much more).
The first letter of 'housed' is 'h'.
'vanda'+'h'='vandah'
'vandah' enclosing 'er' is 'verandah'.
'verandah'+'s'='VERANDAHS'

'in' is the link.

Can you help me to learn more?