1. Not entirely, it has two degrees of freedom. Think of it like a bridge.

2. The opposing springs are normally in equilibrium, so in the absence of forces the center mass moves back to position zero.

3. Think of it like a bridge. The points of contact and support are to the sides and stationary, while the spring mass system is suspended in air or in a vacuum.

4. Is simple enough if you start with two disconnected layers of materials, and then etch the top layer. You could also start with a layer of something like photoresist spincoated on the bottom layer, except for the adhesion points...

An interesting real-life scenario was the possibility of helium atoms being able to get inside the MEMS clock of some smartphones and cause the phone to stop working until enough helium can escape.