Following Mods are compatible with Expanded Japan:
-Radious unit packs [not overhaul, that will crash the game]
-VUS [Vastator Unit Style]
-Readl Armies
-Increased RoF for all Bow Units
-No Realm Divide
-Better Maps [part 1,2 and 3]
-Larger garrison
-Recruitable Generals
-Cheaper Ashigaru
-Increased Farmfood
-Total Carnage


There may be others, those are just all the mods I have ticked on alongside Expanded Japan [actually qbs Beta and Expanded] while playing.