The citadel DLC is very much a side story (unlike Leviathan) and is narratively quite different from the rest of ME3, so it doesn't matter too much when you do it. I lean a bit towards after the credits, since it's a bit of a fun romp that reflects on Shepard and the crew she built (but you could put that as an argument for doing it before too).
the next "y2k" thing vinny is referencing is in 2038, which is 2**31 seconds since Jan 1 1970, and the consequence of using a 32 bit counter (one bit is used for sign).
Most things ought to work fine already, since 64 bit counters are more common now, but there will be some breakage on old storage formats or old systems.
Was there just not enough room in the headset for a hub to consolidate the usb cabling? Or are the data bandwidth or power requirements so insane it actually needs multiple?
Endwashere's comments