Character count for Calendar description

When we export self-service calendar listings for print, we'd like to be able to limit the word count without a lot of hand editing. To do this, it would help if the description field could be limited, especially for those listings that choose a print upsell. Say 250-300 characters max, with a countdown that tells the person entering the listing how much space they have left. 

This could also be a separate, short description field, perhaps, so the long version, if needed, could run online.