1. Is it OK to simply use 1,2,3, ... 12 as the serial numbers? Seems like doing so would keep nitpicker life moderately simpler.
2. The assignment only asks for a string of info about a particular item. My first thought is to simply use a long string of descriptive text for each item. (eg - "This is a book called blah, written by blah, which costs blah to rent , etc.") But this approach doesn't seem in spirit with the assignment purpose to learn all about polymorphism. There would not be anything really different from a video item and a furniture item.
So, I'm guessing I should really define a variety of relevant fields for each class, and build the text string from a particular instance of field values. Is this second approach more in keeping with the assignment goal?