1 In general, the total dissolved solids concentration is the sum of the cations (positively charged) and anions (negatively charged) ions in the water.  Parts per Million (ppm) is the weight-to-weight ratio of any ion to water.
If you refrigerate the rice, and you want to eat it cold, its perfectly fine. People eat cold rice salads all the time. Cold rice pudding is fine. Its just sitting around at room temperature that is the problem.
Yes, yes, a thousand times YES! You can absolutely pre-cook your brown rice and refrigerate it for later use. When Jeff and I make rice, we always soak 2 cups of rice, which makes about 4 cups of cooked rice. Cool it completely, then pop it in the fridge in a container with a lid.