Why is the court considering a writ of mandamus? Hasn't the DHS /already/ been ordered to hold these hearings? Why not an order to show cause why the DHS shouldn't be held in contempt?

Yes, I think worrying about someone scanning the 18,446,744,073,709,551,616 addresses in your /64 is a valid concern.

Here is an excellent panel mounted surge suppressor. http://ep2000.com/index.php?page=industrial

It isn't cheap (several hundred dollars IIRC) but excellent quality.