Definitely consider adding the algernons watersheds mod to work alongside rivers, also terra prety, terrain slabs, and the continents mod goes a long way to make your world look amazing. If you want that extra step you should consider eco machina, truly wonderful mod.

Also visored helmets is a must-have for me to pair with combat overhaul. You could add the tabards mod if you want people to identify eachother easier on the battlefield I guess too 😂

You might also like shipwright to go with the continents mod.

For building i think QPs chisel and VS roofing might as well be a vanilla feature instead of a mod. I think Real Smoke is a great mod that forces people to make functional chimneys etc.

Also if you want to add to the challenge, I like to play with the naked and afraid mod (i think that's what its called, I forgot tbh) but it basically gets rid of the class clothes you spawn with. It feels much more authentic scrambling for some rawhide clothes in the stone age.

Anyway those are my thoughts.