The wider and taller you specify your product, the better your privacy, insulation, and light control. You also need room 60mm x 20mm vary per blind for the mounting brackets at the top, and the optional hold-down brackets at the bottom. Consider mounting the window treatment a bit higher than you'd think so when the blind is raised it blocks less of your view. Add at least 100mm at the top.
For the width, add at least 20 to 30mm on both sides of the glass. Usually the deadbolt latch, however, will constrain the width you'd prefer. The product will usually fall just inside the deadbolt. In the case of a lever handle, the product will slip between the handle and the door.
All products will work on either a wood or metal door. For metal doors, you'll probably need "metal screws" designed for attaching to metal doors, which are normally hollow.