I specifically state sharp cheddar because of the strong flavors. If you opt for another cheese, you may not be able to taste it as much (extra calories for not much of a pay off in flavor).
There are two different kinds of green enchilada sauce. One is made with green chiles and the other is made using tomatillos. They have two completely different tastes. Green chile enchilada sauce is more savory and spicy. Tomatillo green sauce has a tangy flavor without spice.