I would just be careful not to turn Vicenna into Tevinter.
Speaking grammatically, Magii and Vicenii would only make sense if the singular versions were Magius and Vicenius. The plural of Magus is Magi, and I already think that's cool. But I mean it's all rather trivial, isn't it?
I imagined, because of the name, something of a Venice-like vibe for Vicenna. Decadence, color, culture. They'd be a bit more open minded than Areta with a more people-oriented government system. Something closer to a democracy, but I hadn't given it a lot of thought. It was just some place a little more classic fantasy, something more Renaissance Italy to contrast to the weird desert dark ages England vibe Areta's got going on.
Your weird Rita-Maleficent horn picture wouldn't be unfitting, I don't think.