Once content, a considerable number supporting good boy (8)

'once content' is the definition.
'gladsome' can be an answer for 'content' (thesaurus). I am not certain of the 'once' bit.

'a considerable number supporting good boy' is the wordplay.
'a considerable number' becomes 'some' (I have seen 'Undefined number ' mean 'some' so perhaps 'number' could also mean 'some'. I am not sure about the 'considerable' bit.).
'supporting' means one lot of letters go next to another (in a down clue, some letters go below others).
'good' becomes 'g' (abbreviation).
'boy' becomes 'lad' (informal term for boy).
'g'+'lad'='glad'
'some' put after 'glad' is 'GLADSOME'.

Can you help me to learn more?