I've got two questions actually... is it possible to clone from the main stem or top of the plant?... and how important is it for there to be a trimmed node under the surface?

It is possible to clone from the top, It just may take longer to root. the growth at the bottom of the plant tend to root faster. The nod under the soil/cube just gives roots another spot to form. If you dont have it make a little slice along the "skin" of the stem before dipping in root hormone.