Translation:Hij eet minder brood.
Isn't it normal in spoken Dutch to put 'ie' after the verb in place of 'hij'? I was marked as wrong for this
No. In colloquial Dutch (so only spoken) you can replace hij bij ie, but this is not standard. Also if you put the subject after the verb, you change the sentence into a question.
When you use minder and when you use weinig
Brood en broodje have the same meaning
Not really, broodje generally refers to a bread roll and is countable. Brood refers to bread in general (uncountable) or to a loaf of bread (countable).