I'm no expert, I'm just sharing what's worked for me. And brown rice has worked just fine for me. You should definitely cook the rice in the same container you plan to let the mycelia grow in, and be very careful to avoid doing things that could contaminate your batch. Other than that, it's a judgment call. One thing that seems to be the case is that any liquid on the bottom that will drip from one side to the other when you tip it, seem to increase the likelihood of bacterial contamination. But soaking the rice overnight before cooking it decreases that chance, so there you have it.

I haven't ever used brown rice flour, so I can't say which works better though.