What type of flow rate should I recirculate the mash?
i agree with the above; its going to vary depending on the crush and also the amount of grain you have for that particular batch, the surface area of your false bottom, and the amount of liquid. a flow meter, like the additional temp probe, is not necessary at all, but wouldnt hurt if you wanted it.
i try to recirculate the entire volume of my mash about 10 times over the course of the mash (60 min), or once every 5-6 minutes. that means that it takes 5-6 minutes for the water entering the top of the mash column, to travel its way to the bottom. if you have 4 gallons of water in there, that means about 40 gallons per hour, or 2.6 quarts (about half a gallon) per minute. again, this is highly variable, and these numbers are just what i try to do for my system so that i get similar repeatable results. im sure other people have success using completely different flow rates than mine.