I wouldn't get a BK3. I messed around with a BK5 for a while. It was ok, but really you should hold out for the new EA-7, it's improved in every way.
The single USB port which served as both file storage and connectivity to iPad crippled a lot of its potential. And I know there were some unresolved bugs in the style editing workflow. Really the BK's got about the fewest updates of any Roland arranger. And I highly doubt they will issue any more.