You can highlight Friday and Saturday as non-working days by setting both workWeekStart and workWeekEnd options:
As for the size of the cells, by default the Scheduler occupies 100% of the container's width and this way when the container is resized the Schedule (and its cells) resizes accordingly. Therefore reducing the width of the cells would require setting a fixed width of the Scheduler.
See this dojo example
in which both Friday and Saturday highlighting is shown and the Scheduler has fixed width (800) set.