Being rich, we shall have to have a party (4-2-2)
I believe the answer is:
well-to-do
'being rich' is the definition.
('well-to-do' can be similar in meaning to 'rich')
'we shall have to have a party' is the subsidiary indication.
'shall' becomes 'll'.
'have' is a charade indicator (letters next to each other).
'have' means one lot of letters go next to another.
'a party' becomes 'do' (do is a kind of party).
'we'+'ll'+'to'+'do'='welltodo'
(Other definitions for well-to-do that I've seen before include "Financially comfortable" , "Rich; old towel (anag.)" , "Affluent" , "Fairly wealthy" , "Moderately wealthy" .)