It's tidally locked to earth. Earth isn't tidally locked to it. Happens slowly due to gravity and differential mass. Relatively stable satellites end up tidally locked given the time. Pretty sure lack of water/liquids/atmosphere hastens the process.
Mercury orbits the sun every 88 earth days. It spins on its axis every 59 earth days, relative to an outside observer (sidereal day.) That makes the solar day (from sunrise to sunrise) 179 earth days long.
No. I rounded off the numbers. A Mercury day is exactly 2 Mercury years. Which is why it's "in resonance". That means that gravity will speed up or slow down the rotation to keep the ratio stable over time.