Well, she isn't wrong about mistresses being able to have influence in this sort of court politics setting. I just wrote a comment on another series recently about how Madam de Pompadour more or less had the power of a prime minister while she was the King of France's mistress. I'm not familiar with how much the queen did in comparison, so I'm not sure if that's an example to use as far as a mistress having more influence than the wife though.
Meh, that boring nun is going to be the official wife? Hopefully her character develops more but so far there's nothing special about her just a stupid smile on quiet girl with big breasts.
I feel like MC is lacking goals. At first his motivation was to become independent and self sufficient since he wouldn't get an inheritance. He got that with his teacher's inheritance. But now it's like he's just going along with other people's plans for him. And the engagement to the girl is so sudden and jarring, or out of place. He kept saying he's not interested in girls his age, no signs of wanting any romance or starting a family. A stranger hints about marriage and then suddenly MC says OK.