You should really only sharpen once, and base that on your intended output.
If you shoot a JPEG in camera, as you suggested it can apply sharpening depending on your settings. If you shoot RAW the in camera settings typically do not apply. In Lightroom, I would suggest sharpening in the develop module. The develop module gives you much greater flexibility in how you sharpen, and the amount of sharpening you apply. The export sharpening is really just a quick and dirty method if you don't want to mess with the settings in the develop module. I would stay away from this unless you want to maybe use it for quick web or email output usage.
As far as your printer, it really depends on the printer. This might be a good solution, but it might not be. I personally prefer to leave my printer set to default or off sharpening settings and do all of my sharpening in the Develop module of Lightroom or Photoshop.
What is important is that you sharpen as close to the final product as possible, and only sharpen once. You don't want to sharpen first, lose detail and bandwidth, then edit and develop the image. Instead leave it for last as the final step before output/printing/upload.