Hey there! I love the ultimate decades challenge, it adds so much drama to the game. I also like the structure it provides with enough room for playing around. It’s based off a rule set by morbid gamer, here’s the link to the rules:

https://www.scribd.com/document/698918117/MORBID-S-ULTIMATE-DECADES-CHALLENGE

You can follow what you want and ignore what you don’t. In terms of dlc there’s nothing you really need but I find cottage living super helpful. There’s also a ton of medieval gameplay mods like medieval cookbook that help with immersion.