I think the
-severeal Fiefs in good Trade Positions(Middel of the Map and the Edges)
part would be quite hard, but to get the control of ONE city (Veluca, Dhirim, Uxkhal or Halmar sounds good) through diplomacy or war, then defending it with tons and tons of troops and gear from the trade taxes (with open borders) and basically making it a shelter for traders/bandits/outcast. Dhirim free trade area is already pretty much doing the job but maybe another faction would want to manage it differently.
You will need a lot of support though
Maybe the fiefless factions of strat would be interested by such a project