500: a great many pictures? (7)

I believe the answer is:
doodles
'pictures?' is the definition.
The definition and answer can be both to do with creating things as well as being verbs in their -s form.
Maybe there's a link between them I don't understand?
'500 a great many' is the wordplay.
'500' becomes 'D' (Roman numeral for 500).
'a great many' becomes 'oodles' (oodles informally means a lot of something).
'd'+'oodles'='DOODLES'
Can you help me to learn more?
(Other definitions for doodles that I've seen before include "Aimless drawings" , "Scribbled drawings" , "Makes squiggles on paper" , "Idle drawings" , "makes drawings absentmindedly" .)
