So one question I had after reading the fic: what historically is known about why Catherine decided to promote Poniatowski to King of Poland? In the fic the reason given is personal, but I assume that's the personal tip of an iceberg of political machinations that of course you weren't going to show in an "only" 10k fic :)
In addition to the reasons given in the fic (he's from one of the leading Polish aristocratic families BUT he won't have foreign backup (other than hers) to fall back on, you have to consider that the last two Kings of Poland were Saxon Prince Electors who did their best to make the job inheritable (though they failed; Brühl had to spend a lot of money to get August III. elected as King of Poland after August II.'s death). (After August III. died, his son did make an attempt to be a candidate but knew it would probably fail because Saxony had been bled dry, literally, through the 7 Years War which was over only for a year. Poland governed by foreign Kings was the norm rather than the exception - the other Stanislas, Stanislav Lescynski, who ruled in between August(us) the Strong's two terms and was Louis XV's father-in-law, was such an exception, being an actual Pole, but even he was reliant on French backup (and when that wasn't delivered had to high tail it ouf of Poland, with Katte's Dad as his first host in exile at Königsberg; Lescynski eventually ended up getting FS's dukedom of Lorraine and playing host to Émilie, Voltaire and Saint-Lambert). And Poland was, in theory, a large and potentially rich country. On Russia's doorstep. Having it controlled by essentially another foreign power (no matter which one) is not in Russia's interest. Poniatowski, otoh, is someone whom Catherine knows to be strongly attached to her, who is smart in book and conversation ways but not a natural power grabber on his own account, and while his belonging to one of the biggest Polish families means he's just about acceptable as a candidate of royalty he was the youngest son who was never meant to rule, just to make himself useful as a diplomat, which means he didn't grow up considering himself entitled to greatness. He'll know he owes it all to her. Conclusion: from her pov, he's a good candidate.
...except for the part where all the other Polish aristocratic families now hate his guts in jealous indignation and where he actually takes that coronation oath seriously and tries his best for Poland. Which is not the best for Russia.
Re: You should see me an a crown
In addition to the reasons given in the fic (he's from one of the leading Polish aristocratic families BUT he won't have foreign backup (other than hers) to fall back on, you have to consider that the last two Kings of Poland were Saxon Prince Electors who did their best to make the job inheritable (though they failed; Brühl had to spend a lot of money to get August III. elected as King of Poland after August II.'s death). (After August III. died, his son did make an attempt to be a candidate but knew it would probably fail because Saxony had been bled dry, literally, through the 7 Years War which was over only for a year. Poland governed by foreign Kings was the norm rather than the exception - the other Stanislas, Stanislav Lescynski, who ruled in between August(us) the Strong's two terms and was Louis XV's father-in-law, was such an exception, being an actual Pole, but even he was reliant on French backup (and when that wasn't delivered had to high tail it ouf of Poland, with Katte's Dad as his first host in exile at Königsberg; Lescynski eventually ended up getting FS's dukedom of Lorraine and playing host to Émilie, Voltaire and Saint-Lambert). And Poland was, in theory, a large and potentially rich country. On Russia's doorstep. Having it controlled by essentially another foreign power (no matter which one) is not in Russia's interest. Poniatowski, otoh, is someone whom Catherine knows to be strongly attached to her, who is smart in book and conversation ways but not a natural power grabber on his own account, and while his belonging to one of the biggest Polish families means he's just about acceptable as a candidate of royalty he was the youngest son who was never meant to rule, just to make himself useful as a diplomat, which means he didn't grow up considering himself entitled to greatness. He'll know he owes it all to her. Conclusion: from her pov, he's a good candidate.
...except for the part where all the other Polish aristocratic families now hate his guts in jealous indignation and where he actually takes that coronation oath seriously and tries his best for Poland. Which is not the best for Russia.