Your metabolism is higher after your workout so you will keep burning off calories (like the ones you eat) if you walk first, then eat. But if you get fatigued when hungry then try eating something light before the walk, like a banana or apple
I always like to do exercise first like walking. Then have something to eat. I don't like the feeling of something heavy in my stomach like food before a walk or any kind of exercise. Unless I've waited a considerable amount of time.
it depends, are you trying to build muscle or lose weight ? If you are trying to build muscle - you definitely need to add protein after working out. Other then that, if you're doing some type of extended exercise you'll need to have fuel in your tank prior to the exercise so you don't run out of juice.