@Gauvain:
Not necessarily.
Rice production depends on several factors, but in general, a "standard" rice field during the Sengoku period could produce ten
koku of rice. I remember reading somewhere that the size of a "standard" rice field back then was roughly one hectare, so you'd need at least 250 hectares to produce 2,500
koku of rice.
Of course, that doesn't mean the MC's fief is only 250 hectares in size. Those 250 hectares only represent the amount of land that has been set aside for food production. You'd need to allocate additional land for the towns and villages of your residents, pasture for your livestock, and perhaps forests, rivers, and mountains for other resources. That could be another 250 hectares or even 25,000 hectares -- but we have no way of knowing for sure this early in the story.
tl;dr: All we need to know at this point is that the MC's fief has enough room and resources to support 2,500 people.