I'd recommend getting Teleport instead of Exhaust but that's just me. Teleport just gives you a bit more mobility and you already have Wither so it doesn't make that much of a difference (unless you're counting the side-effect).

Gonna edit boots.

pretty good guide. I don't agree with the IE and the Offensive Tree is pretty weak in general unless you are a crit based champion, which Nasus isn't really. But considering you are interested in Crit Nasus i suppose you achieve your goal

Pretty good guide, however I would recommend that you use another summoner spell then exhaust, possibly ignite to get the same killing effect that you want, and instead of ninja tabi you should try out mercury treads, they work better when you are being CCed. I know that you include the treads in your guide, I just think that you will get CCed more then facing a heavy AD team, so they should be more of a priority then ninja tabi.