Yeah honestly just find a feed store near you, the food will last you 2-3 months and you can just seal it up airtight and not have to buy food for a while. Plus you can usually get a 8 cubic foot bale of aspen for $25 which is pretty good.

I really would recommend getting something else for the rats to live in thats open air and not that closed off. But the best thing i can recommend if you keep them in that aquarium is that you change the bedding very frequently. If you let it go to long it will start to get real soaked and will be difficult to clean out of that silicone and the corners.

Yeah i would just make a food hopper like pointed out above and hang it over the side of the aquarium. That way no food is wasted and everyone is happy!