how do you beat a tribal blob that has 20k troops

I am play as sunni (religion) at HISPANIA but I want in the future be a viking (germanic). Then I trying to conquer all the hispania and then conver to catholic (because there is a land there that I can conquer and convert to it) and then conquer all the lands until I reach a land with germanics and convert to their religion. Is it viable or there is a better solution? Thank you very much. NOTE: I don't want to restart the game in another country I like to be ♥♥♥♥♥ because of the guild of assassins at the...

Is possible and viable conquer all the world (entire map) using cheats and mantain my empire even if the people of each region is from different religion and I probably will be one of that they dislikes? and also after it pick another character in my save to play with it?...

so, is it free or partially free? (like with paid features)

I have most of the dlcs