No. It is only compatible with specific L-series telephoto lenses (135mm and above) and select zooms. It will not physically mount to standard EF or EF-S lenses.
You lose 2 stops of light. For example, an f/2.8 lens becomes an f/5.6, and an f/4 lens becomes an f/8.
Yes, autofocus works if your camera body supports AF at the resulting maximum aperture (usually f/5.6 or f/8).
Yes, it features dust and water-resistant construction, matching the durability of Canon L-series lenses.