Generally, popular home occupied by those people first of all? (2,3,4)
I believe the answer is:
in the main
'generally' is the definition.
(I've seen this before)
'popular home occupied by those people first of all?' is the wordplay.
'popular' becomes 'in' (something that's 'in' is fashionable).
'home' becomes 'in' (to be in is to be (at) home).
'occupied by' is an insertion indicator (inserted letters occupy or enter the word).
'those people' becomes 'them' ('they' refers to a group of people).
'first of all?' becomes 'a' (1st letter of 'all').
'in'+'in'='inin'
'them'+'a'='thema'
'inin' placed around 'thema' is 'IN THE MAIN'.
(Other definitions for in the main that I've seen before include "Frankfurters may be dipped here" , "where to find water" , "seaborne?" , "usually" , "Almost entirely" .)