The biggest constraint to his military might would be the lack of money and people, in any case. Military is extremely expensive to maintain. In those times, during offensive war pillaging would help with it, but if you have a large army doing nothing, it will bankrupt the economy. So, Ars would send the people back to their fields, forests, and workshops anyway. He would be wise to have the men train regularly, though, so that they are effective when drafted, should a need arise.
I don't remember the map, or if it was detailed enough, to say whether his village's location is good for an economic hub. Seashore or a large river would have helped with that a lot, considering the times before railroads and automobiles. But then again, he could always rely on his Japanese knowledge for enough innovations to make the place important.