On the flags...I doubt it, in the picture, they look hand painted(i could be wrong though).
As for Yriel as an Archon, i was thinking of using him as my archon as well, however, i think that there will be alot of the Craftworld Iconography on it. Of course, if you greenstuff, you could probably smooth over those...
I was thinking of using him, but i don't know how he'll look on a skyboard...from the looks of it, his feet are stuck into the terrain base.