As far as i know that's a Tanto, not a "ninja sword". It's again another samurai weapon, one made to pierce. The katanas you know nowdays combine that sword's piercing abilities with another japanse curved sword (looks like a more curved katana) that was made for cutting only. 15th century or so a blacksmith made the katanas, a mix of those two earlier swords, that combined the best of both. Ninjas don't have specific weaponry as they weren't soldiers, they were spies and assassins. You could find them using anything you'd find in Japan/China on those earlier eras, which included samurai weaponry.
1. Tanto = Dagger (curved, around 30cm long)
2. You probably mean the "tachi", which is also known as a ceremony-sword and a cavalry-sword (was weared normally, like european would wear a katana, with the cutting edge downside, but just on horseback), this was longer than a katana (120-150cm) and even more curved.
3. There was really no special weaponry for the ninjas, until they called themselves ninjas, then they produced special weapons like the raven-feet, just as an example.
Ask more if you want to know, otherways you can read much 'bout in the internet, i can tell you some things that are true and not, if you want.
BTT:
I really hope they get into the patch, together with the armors, maybe they'll get done better in a time far away.