I don't know if it is too late to answer to this and I just got started publishing it here, but my series The Bard Must Die is composed of NOTHING but public domain characters from world literature. I already have three of the "novels" in the series finished, all of them revolving around the repurposing of a wide range of worldly works - from Shakespeare and Romance of Three Kingdoms to the Wizard of Oz and Don Quixote and beyond.
In order to get all the things I need, I have painstakingly researched public domain and public domain law for about two years now