I use whatever painter's tape I have on hand. Even regular tape that you put on your clothes beforehand to reduce the adhesiveness will work. Since you polish section by section, when I do a one step, I just reuse the same tape for the next section. If you are doing multi steps then you probably should tape the whole car. For that panel in your pic, you should tape around the headlight too.
Can't remember if I said this but I practiced by putting on a glaze with a black pad so I could get the feel for the machine before I started polishing.
Don't forget to do a test spot on a section that is typical of the swirls you have on the car. If your process works there, then it will work on the car as a whole.