Hi Eva,
Congrats on your success. RE: you question about hiking at altitude greater than 8000 ft. I believe at altitude your body uses more energy to provide oxygen to the major muscle groups, stay warm and maintain energy. I tend to eat more calories at altitude but I'm usually wearing a pack and hiking for 10-12 hours a day (25 miles). I do like the idea of a big breakfast with plenty of fat and then to eat about 200 calories an hour mostly of Cliff Shot or Hammer gel. I use this to day hike Mt Whitney, a Whitney double, a fastpack of the John Muir Trail or any ultra marathon at altitude.
I also believe that the shorter event such as a 1/2 marathon can be run on little or no carbs, it depends on what you ate the night before. For me any event greater than 15 miles or 4 hours requires carbs as my primary food source but I do add fat and some protein to prevent stomach upset.
I have seen a few people who can exist on very little food/carbs but they seem to move very slowly and do not hike a lot of miles in one day.
Good luck to you and maybe I'll see you at the Rock 7 Roll, I'm pacing two 60+ year old who are walk/jogging their first marathon!
Maureen