The beta version of the control does not include different themes. It includes OfficeBlack theme only. The rest of the themes will be available in the official version, which will be released in the beginning of next month.
Also, your way of setting custom appointment template seems correct. You can download
our application where this works as expected and review it. If this does not help you, I suggest you send us sample working project to test it.
As for disabling the buttons and checkbox in the edit form - you can apply a style to EditAppointmentStyle property of RadScheduler and customize the whole edit dialog window including the all day checkbox and the edit recurrence appointment button. You can read more about it here
@Koen, thank you for noticing this. We will do our best to solve this problem for the official version.
Your Telerik points have been updated.
the Telerik team