When light above the threshold frequency of a metal is shone on the metal, photoelectrons are emitted. If the power of the light halves, are the maximum kinetic energy of the photoelectrons and/or the number of photoelectrons altered, and if so, how?

When the power of the light is halved, there are half as many photons per unit time. Therefore, the number of photoelectrons emitted is also halved. The maximum kinetic energy of the photoelectrons depends on the frequency of the light, so the maximum kinetic energy of the photoelectrons does not change, because the frequency of the light has not changed.