Yes, and the 20 custom styles are OK as long as you don't use them for sequences that you might send to someone else.
When you load a style from disk it is copied to the Composer. The style is not played directly from disk. It does take some time and is not instant as it would be with a hard disk or SD card as the KN7000 uses. I did not own a KN6000/6500 so maybe someone else can comment on how long the load process takes with that keyboard. Since disk files can contain several different sub files (current panel, panel memory, sequencer, sound memory, etc) the load times can be reduced by only using the files that are needed.