On Jed's Poland, I had to refer to Googer and Vilage to get their opinion. We've come to a couple conclusions to be reexamined and revised. Smallest of it being your claim to rocketry. You can have it, but Googer would be comfortable if you step it back to smaller scaled stuff. Rocket launchers and the like. But no large-scale, long-range missiles.
Vilage also pointed out an imbalanced sort of interpretation to economic woes and fueling a major military overhaul with Dansk. So there's that imbalance.
Of the bigger concern is your claims concerning the Great War. In the history of the real world Russia, Germany, and Austria-Hungary and substantial claim to and interests in Poland. In some way, all three powers were making initiatives before the war to create a Polish state loyal to them, and made sure to keep the region politically divided between them as to use it as leverage against their enemies. They made concessions and set aside promises to the Polish people in exchange for loyalty and for troops.
The political divide of the Polish region between Austria-Hungary, Germany, and Russia would have made the state very volatile and violent. And its position between Germany and Russia would have made it a significant source of violence. On Poland in the First World War:
"The war split the ranks of the three partitioning empires, pitting Russia as defender of Serbia and ally of Britain and France against the leading members of the Central Powers, Germany and Austria-Hungary. This circumstance afforded the Poles political leverage as both sides offered pledges of concessions and future autonomy in exchange for Polish loyalty and army recruits. The Austrians wanted to incorporate Congress Poland into their territory of Galicia, so even before the war they allowed nationalist organizations to form there (for example, Związek Strzelecki). The Russians recognized the Polish right to autonomy and allowed formation of the Polish National Committee, which supported the Russian side. In 1916, attempting to increase Polish support for the Central Powers and to raise a Polish army the German and Austrian emperors declared a new Kingdom of Poland, (see Regency Kingdom of Poland (1916-1918). The new Kingdom consisted only of a small part of the old Commonwealth, i.e. the territory of Congress Poland, although some promises were made about a future incorporation of Vilna and Minsk. The Kingdom was ruled by three Regents, possessed a Parliament and a Government, a small army and its own currency, called the Polish mark. The Regency Kingdom was the fourth and last monarchy in Poland's history.
As the war settled into a long stalemate, the issue of Polish self-rule gained greater urgency. Roman Dmowski spent the war years in Western Europe, hoping to persuade the Allies to unify the Polish lands under Russian rule as an initial step toward liberation. In the meantime, Piłsudski had correctly predicted that the war would ruin all three of the partitioners, a conclusion most people thought highly unlikely before 1918. Piłsudski therefore formed the Polish Legions to assist the Central Powers in defeating Russia as the first step toward full independence for Poland.
Much of the heavy fighting on the war's Eastern Front took place on the territory of the former Polish state. In 1914 Russian forces advanced very close to Kraków before being beaten back. The next spring, heavy fighting occurred around Gorlice and Przemyśl, to the east of Kraków in Galicia. In 1915 Polish territories were looted and abandoned by the retreating Russian army, trying to emulate the scorched earth policy of 1812;[2][3] the Russians also evicted and deported hundreds of thousands of its inhabitants suspected of collaborating with the enemy.[2][4][5] By the end of 1915, the Germans had occupied the entire Russian sector, including Warsaw. In 1916 another Russian offensive in Galicia exacerbated the already desperate situation of civilians in the war zone; about 1 million Polish refugees fled eastward behind Russian lines during the war. Although the Russian offensive of 1916 caught the Germans and Austrians by surprise, poor communications and logistics prevented the Russians from taking full advantage of their situation.
A total of 2 million Polish troops fought with the armies of the three occupying powers, and 450,000 died. Several hundred thousand Polish civilians were moved to labour camps in Germany. The scorched-earth retreat strategies of both sides left much of the war zone uninhabitable."
So things weren't pretty in Poland and they'd be very, very heavily scarred. They'd be coming into independence with a lot of wastelands, a scattered diaspora, many dead, and everything overturned if still not divided significantly between the major powers after they withdrew. Polish history in your app for the Great War needs to be re-examined, it may be alternate history but the history of the Great War here is still close enough to the real world that it can not diverge so much that Poland got out scotch free with only a few cuts and bruises, as opposed to broken bones and a few amputations shoddily and stitched back together.
The situation as Vilage suggests would be considerably dire. The military can be powerful in an effort to resist Russia or Germany from making gains on their former territories and client states, but they'd still have issue. It'd be reasonable to suggest that the post-war depression would be incredibly disastrous on Poland with a young economy as young as it is (even if it could have managed to settle full independence from Germany and Russia well before the War ended). And we'd still have lingering effects of economic recession from then on. Being a neighbor to Russia too it might suffer threat from the destabilizing region, think armed groups noble to anyone using their territories as a forward operating base to re-enter Russia and avoid larger political entities.
And ownership of Dansk isn't going to make anything better, nor occupying Czech lands or Ukraine. Both might as well still come with nationalist resentment still - despite the openness - and the other will have high costs associated with maintaining it, repairing it, and getting up to a "Polish Standard".
I think its RL path to independence might also be worth reviewing.