I just set up khal recently with vdirsyncer too! But to read my Fastmail Calendar. I was a little surprised that the default khal config was not at all to my liking. Here's what I ended up with:

     [calendars]
       [[main]]
         path = ~/caldav/xxx/

       [default]
         highlight_event_days = true

       [highlight_days]
         color = "dark green"
         multiple = "dark red"

       [view]
         agenda_event_format={calendar-color}{cancelled}{start-end-time-style} {title}{repeat-symbol}{alarm-symbol}{description-separator}{reset}

       [locale]
       timeformat=%H:%M

I'd like a bit more colour diversity in the calendar, like different colours for birthdays. And maybe emoji markers (like for brithdays) in the view list.