A paper size template is already defined at each template. The paper size are shown at the top of the window with a selected printer. If the selected printer doesn't have the paper size, the name will look like "4B027455-0B93-...". You need to select an appropriate paper size at a page setup dialog by clicking the "Page Setuup" button.
And you can change the direction of the paper by selecting pull down menu at the top-right side. The preview image in the window will be changed according to the setting.