Happy as model is fine, that is desirable to begin with (9)
I believe the answer is:
satisfied
'happy' is the definition.
(thesaurus)
'model is fine that is desirable to begin with' is the wordplay.
'model' becomes 'satis' (I am not sure about this - if you are sure you should believe this answer much more).
'is fine' becomes 'f' (abbreviation).
'that is' becomes 'ie' (synonyms).
'to begin with' says to take the initial letters.
The initial letter of 'desirable' is 'd'.
'satis'+'f'+'ie'+'d'='SATISFIED'
'as' acts as a link.
Can you help me to learn more?
(Other definitions for satisfied that I've seen before include "as one may be with a second helping" , "Content" , "relieved of doubt" , "served" , "Convinced" .)