Normal.dot is the standard template. I would NOT change this - I'm unsure Word 2011 will rebuild if deleted - but changing this even in the windows world causes issue down the road. Rename the Normal.dot to Normal.dot.OLD for safe keeping and create a new one saving your preferences.
Yup it is always smart to back-up normal.dot. I change mine immediately, however, to reflect how I like my default word document...