How to calculate the temperature of a star
Empirically (I fit a regression on log(mass) vs log(surface temp)), using the table of values in the article on Main Sequence stars, I get a fairly well-fitting formula:  $\mathrm{estTemp} = 5740*\mathrm{mass}^{0.54}$, where estTemp is in C and mass is in multiples of the sun's mass.  Seems to work very well for all but the largest and smallest main sequence stars (and not TOO bad for those).