You should mail every 21 days for the most effective rate of return. So you need to figure out how many homes you can afford to market to every 21 days for the next 12 months. This is the perfect number to start with. There is no such thing as to small of a farm, the perfect farm size is the one you can afford to market to on a consistent basis.
Now for a tip on how to farm for free you will have to visit
my blog post.