Found a good image for our Yen Sid:
[img]http://img1.wikia.nocookie.net/__cb20140318150029/icavalieridellasperanza/it/images/3/35/Yen_Sid_Adulto.jpg[/img]

And here is a rough idea of what his Keyblade Armor is like:
[img]http://fc01.deviantart.net/fs70/f/2012/241/7/9/yen_sid_by_portadorx-d5cx01d.png[/img]

And yes, Yen Sid will be wielding the Star Seeker. I always imagined that it was his Keyblade to start with, but when he retired he bequeathed it to King Mickey, and then later to Sora.