Thunderclast

I'm pretty certain that the bond allows a Radiant to transform the Light into armor. In the visions the Windrunner's helm disappears in a puff of Light, as compared to mist, which is what all Blades, living or dead, turn into.

I believe it is connected to the surge of Progression, as well as his bond with Glys that allows him to see the future. Progression is about growing into the perfected you, which is basically what happens when Renarin heals. He brings people closer to the perfected them, erasing the imperfections of their wounds.

Its like Fatikis said. They are an alloy of the "God Metals" that Cultivation and Honor make. That's why they don't grant all of the surges, it's watered down. 

The honorblades are made out of Honor's essence, so I think what might be happening is using the metal in question tunes you into the Investiture or abilities of the Shard in question. Atium allows you to briefly see the future, as Ati could. Lerasium gives you allomancy, lthe raw power of Preservation. Tanavastium (in sword form) gives you access to the surges.

I'm pretty sure it was Tien, because in the letter Mraize sends to Shallan about Helaran he states that the only member of Amaram's army to bond a spren had been eliminated. Tien and Cenn are really the only people we read about before Kaladin's enslavement.