Military resupplying, maintenance and ammunitions aside, scouts have already been sent around to prospect survey the land for potential fossil fuels.
HR is a bit tricky but with how Alnus thrived getting along with the natives, luring them into the workforce with some modernized incentives should work out fine.
As for farmlands, it'll take a while to develop but Youji will likely get Alnus and its surrounding lands once they win the war. If not then I'm sure there'd be some decent nobles like Italica's that would be more than happy to take in some of the Japanese soldiers that'll remain, and there'd be at least one or two who knows about agriculture.