Advice for Rice balls in bulk
Onigiri (rice balls) can be frozen; that's probably your best bet for long-term storage. They can be simply tossed into the fridge the night before consumption for defrosting, or you can microwave them using the defrost setting if you have microwave-safe plastic wrap. The rice gets dried out pretty fast if you try to store them without freezing them. Note that if you want to wrap nori (dried seaweed) around them, you should do so moments before consuming, as the nori gets soggy REALLY fast even on a fresh onigiri, and crispy nori is much tastier :) 

You mention a "weird consistency", but I'm not sure what you mean by this. If it's the filling getting rubbery, that'll be the microwave; try the fridge-defrost method instead. If the rice is drying out, you need to freeze them faster or wrap them more tightly. 

I don't know about the recipe, but if you have a lot of sauce left over, have you tried using it as a dipping sauce, either for the filled onigiri or for some plain-rice onigiri?