I find the concept of the "Silverstag" faction interesting, but wouldn't something like "Brethren of the Silverstag" or "Order of the Silverstag" be a better representation of it? In short, a naming convention that represents that faction as an organization - because quite frankly "Kingdom of the Silverstag" is a bit much to mull over. As with any mods in the works I wish the best of luck, no matter what the outcome the community always benefits.
Soranus Stealens the Feared of the Silverstag sounds like a cool character - the mans doing what the player is supposed to do, I can rally behind that. Could you give him a daughter we can marry so we can be related to him? Just throwing it out there, none of the vanilla monarchs have any children and I think that would really set your new kings and warlords apart from the rest of the soggy Calridian Royalty. Caba`drin says that this is technically possible, and I was wondering if anyone would be interested in the idea. It was actually done in the Europe 1200 Warband mod, unfortunately they weren't able to get the relation status working and the player didn't have the King listed as his father-in-law.
If you do give the man a daughter, please make her a raven haired, red lipped woman of 21-25 with an ambitious streak. That would be so awesome. If you want to make her look like the daughter of a mercenary warlord turned King then set her up in armor and with a sword, but if you do give her a dress I believe red would do the trick perfectly, or maybe blue?