Re: Unused Vbus pulled to ground or wired directly to ground if not using USB?
In the data sheets "Absolute Maximum Ratings" table, VBUS has a voltage input range of: -0.3 to +5.5V, so a hard short to ground does not violate this.
Just as an aside - when I am faced with "interesting interpretations" of part usage (of which this is not, this is cut and dried) I usually opt to put a resistor in, just make it zero ohms. That way if I am wrong I can just pop the resistor and easily wire up a jumper as required. Much easier than lifting pins or cutting traces. After the first proto, the resistor can be removed.
Hope This Helps...