Go off on tangents with the lives of the band members themselves...For instance..

First three or four papragraphs-summerize the band's impact on music and musicians.

Next 10 paragraphs,delve into the starting origins of the band and band members themselves.

For the closing(4-5)paragraphs you just summerize what youve written and drag on a conlusion.

I don't think you'll need to strain too much for 400 words.Just keep your sentences short and simple.