Planning is for people who can't handle chaos:-). I usually have `300 to 400 lbs of grain on hand, always try to have 2 row, pilsner, Munich light, Mo & Rye in stock, along with about 40 or 50 other grains. That gives me the ability to brew pretty much whatever weird thing comes to mind. The only ingredients that I have found to be a problem with regards to long term storage are flaked rice, which seems to get rancid rather quickly, and liquid yeast, but since most of the liquid yeast I've ordered was dead before it got here, I've pretty much given up on the stuff.
I do have to plan a little bit, say, insuring that one of the fridges is going to be available if I want to do a lager, but I keep a dozen or so kinds of dry yeast and 2 or 3 dozen kinds of hops, so I have lots of options. I try to brew once a week, but as weather warmed and deferred maintenance work beckoned my brewing has been reduced to about once a month.