Nice results, Aaron! I'm glad the formula works for you.
If you find your results are consistently under-exposed, you may be rating the exposure index of your paper a bit too high, in which case a lower ASA number on your meter would result in more exposure.
As for using a yellow filter, that's pretty much guess work. You may want to do a series of calibration tests in daylight, and figure out how best to compensate for the filter.
Enjoy your 8x10 camera. I look forward to more images.