We have 2x1000 gallon tanks (~1600 usable); fill once a year typically about 900-1000 gallons. We originally put in the 2 tanks because we were going to be heating a pool, but don't do that now.
We buy once a year, no club, but we shop every seller in the area (suburban, amerigas, and ferrelgas are never remotely in the running; there's a few smaller distributors who are usually close to a dollar a gallon lower than the big guys). I'm curious about setting up a club buy but suspect with our large fill it wouldn't be helpful, but my neighbors appear to all be on a top-up contract. I've tried to encourage them to at least buy their own tanks but you can lead a horse to water...
This year I was late buying and spent $1.79/gallon in ... I think September. June/July is the best time we've found; I think this year's low point would've been $1.59 vs last year's $1.49.