A) yes and ngons are polys with more then 4 sides and tris are 3-sided

B) No, not really because in the end everything is converted into triangles for rendering so if you have a 50-sided ngon Maya will divide it into triangles at render time. However, you have no control over how it will be divided and so it is better for you to divide it up.

The primary reason to avoid ngons is that they can cause artifacts if the model deforms and the area with ngons becomes non-planar. Also, they can have an effect when texturing.

People sometimes make to big a deal of poly count. In a high poly model you have four kinds of edges - the ones required to define the shape and silhouette, the support edges to define the tension of the edges, then clamping edges (which no one really every talks about), and then some modelers will actually add additional edges in areas so the polys are evenly spaced to improve uv spacing for texturing.