- What sort of chivalric tradition does Anuire have? Or are knights just anyone who can afford a horse and armor?
I expect most knights come from the ranks of the nobility. Knights aren’t just “anyone who can afford a horse and armor.” Wealthy merchants, for example, might have the money, but utterly lack the desire and skills to do so. Better to hire someone else to go die for your money. 
There are strong suggestions from the BR texts that say that knighthood and chivalry are distinctly Anuirean traits (Haelyn is their patron deity, after all, and he is the god of nobility, justice, and war. Sounds like a chivalric model to me!). Using a historical model, it stands to reason that the nobility are the only group with the resources to train and equip knights. Training for knighthood was something begun in childhood, and practiced for many years through the stages of page and squire.
The social status accompanying knighthood would keep it something of a jealously guarded privelage, I think. Nobles and militant temples tend to be the two main sources of knighthood as far as I can tell, and most temples probably induct adult members from the established nobility, rather than raise and train them from childhood themselves.
In more violent border realms, such as Mhoried and Boeruine, I expect the practical necessities of war might allow for more flexible social mobility. Nobles die, and new ones must be raised up to replace them. Moreover, there is simply a greater need for professional soldiers, too, and I expect landless knights in military service are a common occurence there.
Finally, the culture of “adventuring,” so integral to the D&D setting, will certainly have some impact as well. This seems to be one of the main grounds for creating “heroes,” and it’s likely that many adventurers could earn knighthood through heroic deeds in service to a realm. That, and successful adventurers tend to spend a lot of their money on good armor and a sturdy mount, so they tend to qualify in that respect as well. 
- What sort of technological developments have occured lately? I recall someone mentioning here that fireworks have been developed. Magic is rare in Cerillia, surely it being like Forgotten Realms where nothing changes over the millenia would be silly.
My impression of Anuire is that it has been technologically stagnant, in the main, for a LONG time now. It seems that the first century of the Anuirean Empire, under Roele, was the big explosion of human development, the introduction of a Golden Age of stability, advancement, and growth. I expect the Anuirean Empire reached the height of its development some 200-500 years after its founding (rough guess). But after the first few centuries, things slowed down, stagnated, became corrupt, and eventually the Empire falls apart.
550 years later (in the default Anuirean campaign start date, 551 MR), Anuire continues to struggle through its Dark Age. The Imperial City is a shadow of its former glory, since the wealth of a great empire no longer flows through it. The Royal College of Sorcery works to regain some of the lore and power that was lost, and institutions in general seem more preoccupied with preserving knowledge than with its advancement.
You can always write in “burps and hiccups” within this broad pattern…individual inventions and developments by creative individuals. But without a cultural support network (like a Renaissance), I doubt most of these advancements will become anything more than curiosities and oddities - with the exception of advances in warfare, which would be highly prized because of its utility in a violent age.
Hence, general “levels of technology” sem variable to me. I assume most Cerilian realms are several steps ahead in the military areas of tech (arms and armor crafting especially, also miltary engineering, siegecraft, and tactics) than in others, with the notable exception of gunpowder (IMC, I have introduced gunpowder, but it requires Alchemy to make it, and hence is the province of magicians and wizards).
- Is there a set of common Anuirean laws anywhere? Each domain is certainly different, but as a rule of thumb: can a noble get away with murdering a peasant? What sort of crimes usually warrant the death penalty? Are peasants bound to their province?
As Danip said, assume the Imperial laws are the basis for individual realm laws. That being said, though, there were probably a lot of corrupt laws introduced in the latter centuries of the Empire, and the evolution of individual realms’ laws in the last 550 years would allow for a pretty huge variation in the specifics.
In general, I’d say look to the realm’s regent, esp. alignmnet, for an indication of law types (and check out the Book of Regency, too - free download from WOTC). Lawful realms tend to be fairer (one law for all, high and low - law “by the book”), chaotic realms tend to have less over-arching law and more case-by-case judgements (“What book?”). Good realms tend to have less painful/lethal punishments, evil ones love to heap on the suffering to intimidate a populace into submission (I had Jaison Raenech of Osoerde using mass impalements of political subversives and their kin: he lined the major roadways with his victims as blatant warnings to those who would oppose him).
In present-day Anuire, landed regents are very much like petty kings and queens, and have been for over five centuries now. Their laws should reflect this reality of independence and lack of unification.
Also, geography questions:
- Is there any reason Mieres is as small as it is?(it’s surrounded by uncontested lands) Do they have regular contact with the Andu?
IMC, the lands west and south of Mieres are lifeless wastelands, inhabited only by roving bands of the undead. This “Dead Zone” creates constant problems for Mieres, and is absolutely uninhabitable by humans or any other living creature. Arcane magics are useless in this place without mebhaighal. There is no barrier between the physical and shadow world here, though this matters little as only the undead surivive for long in this place. The Wastelands are sometimes a popular area for short-term expeditions by crusaders and militant zealots who like to beat up undead (paladin training grounds).
This cursed zone also extends far out to sea, creating freak violent weather and claiming careless ships and crews to become undead ghost ships preying upon the living who venture too close.
Makes exploration south by land impossible, by sea possible only with some really expert deep-ocean navigation.
My explanation for this is that the blast at Deismaar was mainly shunted south by the dying gods - or at least Azrai’s blighting essence was. Perhaps his deep connection with Aduria drew his energy in that direction, who knows?
IMC, Mieres establishing contact by sea with the east coast of Aduria (south of the blight) was the beginning of a brave new world, one in which Mieres eventually massed an army and forged an empire out of disparate city-states there.
- What are on the islands surrounding Cerillia? Albielle is a haven for pirates, iirc. What about Cael Corwynn, Baerghos, and Dantier? There must be a reason why they’re unsettled, certainly.
Dantier? No idea, never really touched it.
I have Caelcorwynn as a magically warded isle (always under the Ward province realm spell), something like an elven Avalon. It is inhabitated by the Sidhelien refugees from the Erebannien, who have become a rather unusual elven “tribe” cloistered on their island sanctuary. They have a naval version of the Gheallie Sidhe - the Corsairs of Caelcorwynn sail small, swift ships, manned by Sidhelien warrior-sailors and elementalist mages, and prey upon human shipping in the sea-lanes of around southeastern Anuire. They take pains to leave no witnesses…meaning no survivors of their attacks. Vicious.
Albiele and Baerghos I had as human pirate havens, though Baerghos’ forested, hilly interior was home to some nasty beasties who kept the pirates pinned in fortified villages on the coast. Albiele was a nicely developed little pirate realm, complete with land, law, guild, temple, and source regents (1 province, but hey - they were kings of their little world) - at least, until Mieres came and cleared them out altogether (IMC).
Osprey
