I went with a wider tape. Personally the wider the better for the rear arc on the coupes. I think I went with the next biggest size from bmwshadowline. I have a red coupe and went with the matte black. I like it and i think it looks sick.
Having said that as far as the install is be patient, a second pair of hands helps. Mine came out great for the bottom pieces but the rear arcs got some small flaws if you get real close. Vinyl has held up in all kinds of weather over the last year no problems. 1 roll with some failed attempts was enough for my coupe.
To conserve vinyl you can get the 3" wide strip into two 1.5 inch strips for some of the length to do the bottom pieces.
YOU WILL NEED all the width you can get for the rear arc tho