Currently, I am playing as the white huns in my first campaign and I just finished off the Sassanid empire and numerous of its vassals. What do you think I should do next? Also what mod recommendation. Thanks a lot in advanced!

Maybe try one of the roman empire factions, playing as the eastern empire can become a power fantasy towards the end, and trying to hold the west together throughout its fall can be extremely challenging but rewarding, also for mods try the 1212AD mod, its really well made and is still receiving updates regularly  

Burn Eastern Roman Empire and Arab kingdoms to the ground - you are immune to desert attrition, use this as your advantage. Once done, finish off remnants of Western Rome and destroy petty barbarian kingdoms :)