The dynamics in Wiendrj will become clearer as we get into Game 3, but fragmentation is overwhelmingly likely there when the Hegemonic boot is removed. So yes, a cosmopolitan Rim-and-Southriding state could potentially draw in some of the southern Wiendish clans.
Moving out of the southern highlands (the Zdzesin to Szeric arc) to fully incorporate the lowlands around Alsztyn and Stezyc could be logistically tricky, though. Those are some of Wiendrj’s most valuable and populous territories, but dependent on grain imports up the river. Even if the population was reduced to what the local farmland can support, they’re still much more easily accessed from the east than reinforced from the south, so you’d be vulnerable to invasion by whomever holds the Shayard Reach.
Your second map, where you hold much of the Westriding and some of the western Reach, would solve that problem…but in that scenario, it would be pretty hard to defend your eastern flank within Shayard. An ever-shifting border somewhere between the Rivers Eddern and Fyrne would I think be the most likely outcome. Your attention and military strength would need to be focused there, so if any of the Wiendish districts wanted to break away, you’d not be able to do a lot to keep them in your realm.
I don’t think that’s going to happen in the wake of an imperial collapse, especially one where the pre-collapse “police” had been so broadly corrupt and extractive. I’ve unfortunately seen close-up how hard it is to reform a force like that under circumstances of ongoing civil strife (even in the present day when we have lots of successful models we can consciously work towards). Getting your Hegemonic police force to the point where it can do the “keeping public order” part is a Herculean enough task.
You could decree that for certain crimes, guilt can only be established by a jury of peers, not by a judge. The local magistrate (whatever form that takes post-Hegemony) would then be responsible to convene ten people deemed to be peers of the accused; in the absence of an effective state investigative arm, the juries would be “self-informing, in that individuals were chosen as jurors because they either knew the parties and the facts, or they had the duty to discover them.”
Independent from the state you’re establishing? Pretty tough, I’d say. You can reorient the system away from presumption of guilt and confession-extraction (an orientation that many law enforcement systems have kept until shockingly recently), toward presumption of innocence, but given the dearth of potential lawyers I mentioned before, I think your system isn’t going to have enough legal specialists to staff both the state system and a hypothetical independent bar big enough to be meaningful. Maybe if you end up governing a micro-state, like Mara’s Vatican Switzerland?
In relation to lawyers? You can found institutions to teach your new deNapoleonic Code, but with everything else going on in the imperial collapse and war, I don’t think you should expect those to be high-output for a while yet.
You can invest in various schemes to promote mass literacy, and we’ll see how effective those can be. As we see in India’s case or China’s, even with all the technologies of mass literacy operating in a modern state, it can take more than a generation to get to 50% from a similarly low baseline. In the post-Hegemonic context, progress will surely be slower than that.
You will be able to go with the existing religious code, reinterpreted to various degrees; to institute a new code based on Angelic revelation; or to try to roll out a post-revolutionary code unrelated to the Angels. There’s no “common law” in the Hegemony other than the records of priestly outworking of the canon through the centuries, so any secular law code you implement will be statutory/civil.
Pretty basic, I think, and pretty vulnerable to capture by local elites. You could try to institute a secret ballot (with the challenge of getting recognizable symbols for each candidate so the illiterate can take part) or go for choice by public voice vote. Depending on the size of your realm and overall anarchy levels, you might be able to get central representatives out to witness a decent sample of the moots that choose the local leadership to make sure the choice is being made fairly.
More likely, given the limits on central admin capacity, you’d simply be decreeing that every community/urban neighborhood of a certain size has the right to choose its own leadership through the choice of a majority of all recognized adult residents, and that this needs to be documented and your central government informed. You could regardless expect to have a huge number of cases where local elites complain that their rivals rigged the choice.
Because of the logistical limitations on vote collection and counting, if you wanted to have representation in your district, provincial and/or central lawmaking bodies, I think you’d need to have those representatives chosen by a body of local representatives from among their number. I don’t think any post-Hegemonic state is going to be anywhere close to the point where it could hold credible realm-wide elections, or really elections that go beyond (max) a few hundred participants at a time.
The Hegemony has achieved early industrialization, all based on blood magic – high farm yields, large scale production of iron and textiles, a continent-wide canal/riverine transport system. As with the Roman collapse, a lot of that will be put at severe risk simply by the breakup of a single political system into competing blocks, even if the rebellions that bring it down aren’t also trying to reduce the use of blood.
Spinning jennies have been invented, so industrial-scale textile production should still be possible with the mills adapted to Whendish waterpower. But the Hegemony’s iron/steel production methods have relied on Theurgic mass production of trees and charcoal; use of mineral coal is a curiosity, done nowhere at scale. (Though as Erjan will tell us in a Ch 3 aside, the Magi of Halassur have been experimenting with spending less of their energy on charcoal and more on “anthractic earths,” which are present in some arid areas of the Empire in much greater quantity than trees). The trade networks that underpin industrialization would half-collapse if canal maintenance and river channel dredging had to be done by manual labor, or barges and boats could only travel at the speed of horse or the mercy of natural wind. (Grand Shayard sits almost perfectly in the middle of the world’s doldrums.)
I mean, it’s totally tainted, but so is “Goete” and you can still pick that. 
It’s a Gutenberg-style movable type press, not a cylindrical one (that tech won’t be invented in the game time), with priests able to operate it either manually (with the Britannica-mentioned rate of 250 sheets per hour) or in the rare cases where faster production is needed, with a Theurge exerting pressure on the plate.
The gameworld has the concept of the “rights of nobility,” and of special “rights and liberties” granted to particular groups; when those are disrespected, the member of the group can appeal to the local authority to enjoin the respect of their rights. (Usually, as in the early modernity of our world, this happens in property disputes.) The idea of universal rights and liberties that apply to all humans isn’t (I think) so far over the intellectual horizon that a MC/their friends couldn’t come up with it and try to encode it. So yes, you will be able to try to enact universal rights into law. We’ll see which rights end up being thinkable, and anything resembling enforceable.
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Shayard didn’t become a naval power until it used cavalry to conquer the Coast and Aveche, and never matched the Erezziano city-states’ experience and power at sea even then.