Like you, I decided it made a lot more sense to stock a selection of primary colors from which I could blend most beers, rather than focus on specific quantities of each malt for each brew. Although I've never really thought about it this way, I suppose you could divide my malt stocks into four tiers: 1) 50lb sack purchases; 2) 10lb bag purchases; 3) stuff that it makes sense to buy by the 5lb or 1lb bag; 4) stuff, typically adjuncts, that I can buy at the grocery store for far less than LHBS prices.
You're brewing very different stuff than I am, so you'll quickly lock in what your primary colors happen to be. I write the following about my brewery in the hope that it will assist you in organizing your own thoughts.
Much like yourself, I settled on 50lb sacks of Otter and German pils as my tier one malts. At a dollar/pound basis, these are easily the cheapest malts in my brewery--which allows me to splurge on some excellent examples of Otter and German pils. I am certain that I'll reliably plow through these grains in a timely fashion, so they're well worth buying by the 50lb sack. I've learned to blend these to approximate other base malts, but there's no ratio of Otter and pils that will be a dead ringer for Great Western two row, Golden Promise, Rahr pale malt, etc...so what? It's part of the house flavor of my brewery and I'm cool with that. I suppose I could reasonably also run a bag of domestic two row, but... I don't see the point. I'm happy with my ratios and the result doesn't seem to justify the bother. Hint: sometimes a bit of boring old table sugar is helpful to dilute the characteristic flavors of German pils and Otter when you're aiming for a very neutral base grain.
Tier two is the tricky one! These are malts that I use with a very high frequency, but I've learned that I don't reliably use them frequently enough to justify the 50lb sack. Vienna, Munich, malted and torrified wheat, and patent malt all live here. I tend to brew for the seasons, so mid-winter and mid-summer, I sit down and write a big order to an online shop based upon what I know I reliably enjoy for the coming two seasons and what I'm interested in researching/mucking around with. Sometimes I'll guess right, sometimes I'll have to put in a smaller supplementary order, or, like this year, I'll end up with 20lbs of unused wheat malt because I went on a colossal CAP kick this spring and summer when I'm normally going nuts for hefes and American wheats. Fortunately, I've found that year-old malt, when stored correctly, is just as good as any other, so you don't have to stress about over-ordering. My options next spring will be constricted a bit. I like wheat beers in the spring, so it's no biggie.
Tier three is pretty easy: These are your character malts that define certain beers that you brew seasonally, or use in small quantities. For me, it's UK C-60 and 80, Carastan, US C20, C40, and 150, Melanoidan, Biscuit/Victory, brown, and the chocolates. Based upon their velocity, I buy some of these by the pound, others I'll get two pounds.
Tier four is simple: Flaked wheat, oats, rice and corn are cheaper at the grocery store than their identical counterparts at the LHBS or online. Rather than waste storage space, save a few bucks and let the local super market store them for you.
As a final note, and certainly the most important note, get proper storage vessels for your grain. My initial attempt at establishing a grain library was undone by weevils (idiot West Coaster living on the East Coast mistake). Get proper storage vessels with gasketed, air tight lids. Yeah, they're expensive, but they'll save you money over the years.
)
