well, brakes are easier to replace than a tranny so id suggest using the brakes...trust me.
shifting in nuetral is just coast...it is fine. shifting back into gear is okay as long as it is not reverse when you are moving foward.
hell, you can even shift it into 1st at around 40mph and it'll probably just shoot up to 6k, lol. my friend did it beforte in his camry, hahahah.

anyways, for the a/c...once you hit the button and it doesnt light up than you are not using it.

idk, some people say that they have only seen a 3mpg effect from using a/c. fan speed is fan speed, i dont think it'll affect the mpg. best is to just use a/c when crusiing or coasting.

the recirculation doesnt affect mpg either, whent he cabin is already cold, it just reciculates the cold air as opposed to the hot/room temp. air outside.

hope this helps.