1. In the Rashi at the bottom of amud aleph, Rashi gives the numbers of dayanim for dinei mamonos,nefashos, ibur hashana and kiddush hachodesh. Why does Rashi go into a reason only for kiddush hachodesh, and not quote our mishna for either kiddush hachodesh or any of the others?
2. On amud beis, Rashi says "mah lanu lachus al shor hamuad". Why does Rashi imply that only a shor hamuad can be a shor haniskal? Even if we restrict shor haniskal to mazikin, and not include rove'a venirva, couldn't a shor tam also be niskal?
1. Rashi first lists Mamonos and Nefashos which are, as he points out, "Min ha'Torah." He then lists Kidush ha'Chodesh, which is only supported by an Asmachta. He therefore quotes the Asmachta, as it is not a source which is discussed in our Masechta and is not clearly derived "Min ha'Torah." Ibur ha'Shanah, however, is discussed in our Mesechta at length, which is why Rashi merely refers us to the earlier Daf.
2. The Rashash asks your question, and implies that Rashi is just giving the common case. A Shor Tam, as you noted, could also be a Niskal. [He also includes Rovei'a v'Nirva.]