You came to the right place! There are some
seasonal mods as well as a big add-on called
Grim's medieval core. It puts a whole new set of options in the game menu as well as unlocks debug interactions on sims. I do not know of any traits or quests though

There has never been a big community for modding in TSM and I do not think anyone has even figured out how to make new gameplay. There might be armor unlocked somewhere, but you can wear any armor you have by just clicking the change into option from your inventory. If you right click any sim you can control them, give them armor, and then have them change into it, but it might not really stick once they go to bed or despawn. I recommend going through
mariacherry's blog on tumblr to find a bunch of stuff especially as she is actually still active! I think there was a discord at some point but I am not affliated. If anyone has a discord link let me know!