I have never read a book in English or Japanese about the demographics of each province during the Sengoku. I would use Shogun Total war and base the population from how much the province is developed. I think it would be best to have Japan start off with the provinces already made. And making sure that they all have atleast one citizen. I think you could cut the number of clans in half, since having all of them there wouldn't be historically accurate either. I would keep the main clans. And make the lesser daimyo into one unplayable civ. Or limit the lesser daimyo and make them unplayable with no unique features. I have really good props (helmet and armour) for Date Masamune, Uesugi Kenshin, Takeda Shingen.