Eugene,
I tend to buy wood in at least 200 to 500 board feet mini lifts at a time. I plan my work in blocks of 3 or 4 months - and then make sure I have everything here before I start. But, I also look for deals, and if the price is trending up on species I use regularly (like recently maple and walnut) I order a full lift. I got in almost 1000 bf of hard maple a few months ago. Ill burn through that before the end of the year.
Some stuff like Butternut, is just plain hard to get so I keep a few hundred feet in stock.
I can get most species within a week. But some take 2 to 3 weeks for my supplier to get and then get to me. So I stock a lot of my own wood to have easy and immediate access.
ALso, in the winter months, I have to bring the lumber inside the heated shop for 2 to 3 weeks to aclimatize.
Furniture making is not something where I would buy lumber off the truck and immediately turn into product. Even in the summer I let it sit in the shop for a while to get aclimatized.