I would have some some sort of constitutional monarchy with a parliament or congress to keep things fair. Not sure how prevalent the idea of democracy is in Thedas, but I suppose this will do. Thedas seems to be used to monarchy, so this seems like a good start.
There would be total religious freedom, save for perhaps the Qun. I am not overtly hostile toward the Qun, but it just wouldn't work. The Qun is a form government and economy as well as a religion/philosophy. Ideally, the nation would be officially secular. In addition, mages will be trained in academies with more freedom.
Other races would be allowed to live in the nation after a few years, and would be allowed to hold office, provided they are elected. The only reason a human, dwarf, or qunari would not hold office would be that they were not elected. In fact, we might need a few humans to help us get started, seeing as no elves would have experience in government.
The nation would trade and negotiate with any willing to do so with it.