I will pick off the one that is easiest for me to answer:
I.E. just go to Sam's and buy rice, beans in the bulk?
Traditional "dry goods" like beans, rice, white wheat flour (whole wheat will go rancid, so you can either vacuum pack it, or you can grind wheat berries on an as-needed basis), powdered milk (preferably vacuum-packed as it does spoil), lentils, dried peas, and that sort of thing, are your best bets, far and away, for convenience and cost-effectiveness. This is what most of our ancestors did, before refrigeration and regular supplies of groceries at the store.
If you have restaurant supply grocers, like Cash and Carry, they carry more variety of staples than the warehouse supermarkets. That's where I find things like lentils and split peas.
How about wheat, where is the best place to purchase that?
You mean like wheat berries (whole wheat kernels, intact?). That might be tricky for most folks...mail order but then shipping gets expensive.
Hopefully someone else can chime in...