Hi Dayna, These tacks are about 5/8" head. Upholstery supply places have dozens of styles and finishes. A hard rubber mallet is important for putting these on. On the straight lines, i would lay a piece of painters tape along the line that had the spaces marked on it (just little tick marks with a sharpie), then would hand set about a foot at a time, poking the nail thru the faux leather. because of the layers of batting underneath, they'll kind of stand up for you . then i worked my way down the row, grabbing the nail w a pair of needlenose pliers and tapping it halfway in, on down the row. once they were mostly set, i'd go down the row and whack them the rest of the way in, leaning the mallet head slightly one way or another to keep them going in straight. You kind of get the feel for it, practice on a scrap/sample board.
Door must be solid, no hollow core doors for this! I also used a chalk fabric marker to mark the lines sometimes. Happy to help,