Supply required items, nothing is initially excluded for a balance of interests (9)
I believe the answer is:
equipoise
'supply required items' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'nothing is initially excluded for a balance of interests' is the wordplay.
'nothing' becomes 'O' (O resembles 0).
'initially' indicates taking the first letters.
'for' means one lot of letters go next to another (I've seen this in other clues).
'a balance of interests' becomes 'equip' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
The initial letter of 'excluded' is 'e'.
'o'+'is'+'e'='oise'
'oise' put after 'equip' is 'EQUIPOISE'.
Can you help me to learn more?
(Another definition for equipoise that I've seen is " balance".)