Whole grains will store longer than milled, with the milled types you'd want to look into the old freezer storage option to get added shelf life. Or something else to store it in that will seal. Whole grains can protect themselves from going stale, once it's milled or cracked that natural protection is gone. Same with pellets and crumbles as well, no protection, but the bags are designed to keep it fresh.
I'm in a feed co-op as well, we all order at the same time, I think we're up to about 60 people now. Initially they offered a milled 17% protein (non-GMO) layer feed, but now that we're over 2 tons of buying power, we get a custom whole grain mix layer with 19% protein.
It would be cheaper if it wasn't bagged, but with it getting split up the way it is across the city, we need it bagged. Someone needs to buy a silo!
I store mine in galvanized garbage cans after squirrels decided they needed to taste the new feed mix. Never an issue until we switched to the new mix, now the squirrels know about the sunflower seeds and corn kernels.
Birds are doing great on the new feed, very little waste. They only thing I add now is meal worms since we're fresh out of crickets in the yard until the weather turns. The birds aren't fans of winter... grass is short, bugs are gone, and they don't care for the damp. Spoiled they are!