On page 21, on the bottom-right it says "The years-long siege of Arlathan ends when Tevinter is said to sink the city into the ground using blood magic." If Arlathan was a huge city it's highly unlikely it would have endured a "years-long siege" without its inhabitants resorting to cannibalism and without suffering from epidemics, when the attackers would catapult diseased corpses of animals into the city. A siege of a large city would have hardly lasted more than a few months, especially if the city was completely cut off from food and water supplies. A side question - given that the elves hadn't met hostile civilizations before, would their cities even be surrounded by walls to begin with?
That would depend entirely on the layout of the city, the population of the city, the supplies of the city, the infrastructure of the city, the supplies of the sieging army and a truckload of other factors, ALL unknown to us. But in a world like Thedas, with magic and healing, launching dead cattle over city walls are probably not as efficient as in our world, since the enemy mages could, theoretically at least, quickly eliminate any potential contamination.
Anyway, for all we know the Siege of Arlathan lasted for a couple of years. And that is all we have to go on.
On page 76, it says "Powerful, noble mages form a legislative body known as the Magisterium" and also "Archons rule by divine right, a tradition that predates the imperium" -- The common meaning of "by divine right" is "deriving a right to rule directly from the will of a deitiy/deities". If this is truly so, then the Archon shouldn't need a "legislative body" at all, and the Magisterium shouldn't function as more than a king's council with final authority sitting with the Archon.
The Roman emperors also had a senate. The power of the senate varied widely depending on the personality of the emperor on the throne. I'd imagine it is similar in Tevinter.
On the same page, from the description of the Magisterium it follows that its members are no more than 20-30 people (7 coming from the Circles of Magi, plus every grand cleric plus the Imperial Divine, plus whomever the Archon has appointed). Doesn't the Archon's prerogative to appoint new magisters allow him to manipulate the Magisterium's contents and its decisions at will? From the described rules it follows that if he wants a certain move passed, he can simply appoint enough of his own cronies to ensure the move has enough votes.
Almost 50% of the Magisterium consist of people the Archon has no power to appoint (the clergy and First Enchanters), the last 50% he can, in theory, appoint at will, though the Magisterium can probably pressure him to appoint certain individuals over others.
On page 78 - "Liberati can join a Circle of Magi or serve as an apprentice in a trade. Liberati may also own property, but they cannot join the military and rarely have a say in governance." -- this puts the Liberati in a position similiar to that of Jews in medieval and early modern Europe, with the exception that Jews in most places weren't allowed to own land either. If a Liberatus is exempt from holding any public office or military rank, the only venue remaining for him/her would be amassing wealth. I wonder if there isn't a thin layer of Liberati who have become superbly rich.
Probably. Though I think the common Tevinter attitude to slaves, even of the ex variety, is much worse than anything to Jews ever faced in medieval times.