The most important ting here is ESD protection, i blew the fuse in mine, but this was due to experimenting late at night and then reversing polarity of the homemade USB charging system........

So i would say put an ESD protection on the data lines and that should be enough.

NOTE: I fixed my USB with removing the fuse and soldering a thin wire in there in stead, and yes this is not the best solution at all, but it has worked for some months now, of course i only use the USB connection once a week on average due to my charging system.

I bet i will have the N900 that lasts the longest in the USB area