Hi Jörg, glad you're using it in more depth!
"Recurring" tasks are much simpler than you think - they just remove the "Completed" checkbox, as a recurring task will never really be done.
Deselect "Recurring", and the "Completed" box comes back.
Reminders are a little different... If they're selected as "Daily", "Weekly", anything but "Once", they will fire on that schedule and every day after until they're deleted.
Items with due dates show up on Dashboards as due that day, all day. I've noticed a couple of bugs with the calendar plugin I use, so I'll tackle them soon.
Thanks,
David.