The 2 piece is indeed 2 separate pieces. The outline will cut the shape of the cookie and then the separate stamp piece will push in all the inner details separately.
The 3.5" cutter is 3.5 inches tall and 1.25 inches wide. All of the different sizes are proportioned to this same ratio. All versions of the cutter will cut approximately .5 inches deep (or 14mm).
Hand wash only! Do not wash in dishwasher!