For charging, I use one of these so can charge two devices at the same time ... I'm sure there are others but liked this one as it will flex and really stays plugged in the way its designed; have used it in 3 different cars
http://www.amazon.com/gp/product/B00YDK1HYG?psc=1&redirect=true&ref_=oh_aui_detailpage_o00_s00
I use the single USB with a memory stick for music, on our '12, doesn't show the album covers but does a decent job listing the albums and songs; on a PC a USB splitter might make sense but on a LEAF its low power and really designed just as a data out connection; if you search a few more threads you'll see more info folks have posted on this