Hey Michael, this actually comes with everything you need. It does include the temp sensor and harness. The sensor is 1/8 NPT and it includes adapters for 1/4 NPT and 3/8 NPT as well. For the face plates, they give you 6 gauge faces: water, oil, and transmission temp, each in both black & white, and it also includes both black and silver bezels.
You'll just need to add an adapter for the sensor along with a mounting solution for the gauge itself, both of which will of course vary by every vehicle/application.