I buy sacks of 2 row, pilsen, vienna and munich along with 10-20 lbs of some other grains I use often. For storage I have three vittle vaults and an assortment of food safe buckets and containers. They're stored in the basement storage area where my brew gear and laggering chest keezer are located. It's generally 68-70 in there year round.
I haven't been going through the grain as quickly this year but I've never felt like any of the grain has gotten stale. At one time I started using the inventory feature in BeerSmith but I haven't kept up with it so I can't say for certain how long it takes me to go through a sack of grain. When I started looking into buying in bulk the general consensus seemed to be that stored in an airtight container grain should be good for more than a year. I doubt I've ever had any around that long brewing mostly 10 gallon batches.