^^ It all depends on what sort of costumes you would like to make, be it goth, fantasy, punk, sci-fi, lolita, jrock... and if you want it to be dramatic, elaborate, cute, sexy... Determine what you are willing to wear and make and go for it!
Of course, if you ever get to showcase both pairs together, oppositing costumes come to mind. Try visiting some CLAMP galleries for X 1999 and Chobits art for ideas and inspiration for such costumes ^_^.
Let us know how this project turns out