My first suggestion is adding hot oil that kills more than rock but is more expensive for wall defense. I also think that ballistas should be used for killing boss monsters rather than killing more orcs due to their piercing nature. I would also like to add cannons or catapults for wall defense. It would also be nice if enemies also use weapons to either damage the wall more effectively like catapults or fire arrows to kill defenders before the wall is breached. You could even have to make a decision on which group of enemies to focus on: the one attacking the wall or the one attacking defenders.
My second suggestion is helping characters also improve their relationships. After all, these characters should feel grateful that their lord is helping them with their tasks. Gaining relationship points from helping characters should be minor compared to chatting with characters though as the former is for work while the latter is from meeting you although it is not related to work.
My third suggestion is adding magic both for fighting and the economy. We are playing a fantasy game where orcs existed but we don't really get to use magic except time travel.
My fourth suggestion is that we gain resources/abilities if we max out each character's relationship. Like gaining more food if we max out Mollie or gaining more charisma if we max out Noah. It would be also nice if each character had a unique way of providing fighting power like Tillie making hunters serve as soldiers as well, Marian providing church paladin out of loyal followers, Roheisa providing slave soldiers out of slaves, Victoria providing assassins, Sylavia providing mages, Laura providing all-female bodyguards, and so on. And they are not generic soldiers as each provides unique abilities like Tillie's hunters can shoot arrows and gather resources through hunting, Marian's church paladin increases charisma and respect through holy magic, Roheisa's slave soldiers may be most cheap but have demerits like decreased charisma, respect, and may rebel if not kept in check, Victoria's assassins may be able to fight like a generic soldier but they would be more effective at spying and assassination, Sylavia's mages are effective fighters but they cost more money, and Laura's female bodyguards providing more sanity due to more protections and essential to prevent an assassination that leads to a game over.
My fifth suggestion is that we gain resources/abilities if we gain trust from Lord Charles, Lord Steven, Elves, and Dwarves. And gaining their trust gives unique resources that only they can provide. Like elves give special bows and arrows with their nature magic or dwarves give muskets and cannons.
My sixth suggestion is that we have slave characters from Roheisa who are not generic slaves. It would be interesting if the lord treated them as equals or not. This could have its own plot line as it determines whether the lord is moral or immoral and thus determines the ending.