1) Swords? I can't see any real application for them today. Bayonets maybe, as they can be useful for things other than combat, but a sword is too big and heavy to justify carrying around for anything.
2) If you mean things like 5.56x45 mm and 7.62x25 mm the first number is the bore diameter and the second number is the total case length. However, they can vary and sometimes neither of the numbers have anything to do with the diameter or length. It all depends on the cartridge. There can also be numbers/letters after the cartridge name that identify its type (ball, AP, blank, tracer, etc.)
3) In theory, I guess, but it's a convoluted way of using, basically, a stun gun.
In the cramped, close quarters where you're likely to meet an enemy in modern close combat, a sword isn't much better than a bayonet, even if you have the space to properly use it.