I try to avoid traversing the roof with coax. It provides a place for debris to get caught and then create a dam to water and ice. I prefer to run down to the edge and then proceed under the eve or soffit.
But as I look at your photo, I wonder if a set of wall brackets would be even better. I've yet to have any leak issues with a mast supported by wall mounted or gable end mounted brackets.
Re. grounding, I'd suggest you not add another ground rod, but run the mast and coax grounds to the existing electrical service ground. You want to use the same ground system any way, and an added rod would require that you tie it to the existing ground system to ensure there is minimal voltage difference between the existing and new ground rods.
http://forum.tvfool.com/showthread.php?t=901 (summary at post #20)