The stock filters will last for a long time if you soak them every 20 or so roasts in a cafiza solution. I rotate about three of them, sometimes remembering at 20 roasts, sometimes not. Machine just keeps on chugging.
Tex--as for batch size, I stick to 200-227g, as that gives me the most control to speed up as well as slow down the roast. More than that, and I feel I have to run at full power to get to 1st in a reasonable time, which keeps the environmental temp (ET) too high, and makes it difficult to stretch between 1st and 2nd without lowering ET.
I run the fan at 25% at the start of a roast, bump it to 50% and keep it there about 4 minutes in.