Just because something can go wrong doesn't mean its likely to go wrong. The n54 internals are way over built for what you are going to be asking out of the engine. Most of the things that will go wrong are wear items that will need replaced anyway you just might have to replace them a little sooner is all. There are tons of modded n54s and very few major problems as a result and most of them were people that track there car.
"And just one question I might ask yah, and it might sound like A disaster, can you make this thing go faster?"