I have used the run 10 walk 2 strategy in 2 marathons and completed both in about the times I expected. Walking before you exhaust completely enables you to get going running again. I found we achieved the same times training a half without the effort needed previously. Only problem is the walking in early miles as felt everyone looking.
My take on nutrition for a half marathon is first as how long will it take for you to run it? The widely accepted time for running without taking on extra fuel is 90 minutes. This is OK for faster club runners but not if you are going to be out there for over 2 hours. Not suggesting gels every half hour or such just an odd one at 90 minutes to get you home.