It has been about ten years since I grew shrooms. Now with that said, I have a few pointers for you. I do not recommend buying prepared brown rice powder. It is way to fine for your purposes. It will cause clumping. We want to keep this as close to a soils texture a possible. Fast colonization of mycelium and high water content are crucial to success, and a high yield. You are going to want to grind your own brown rice flour. Use a cheap electric coffee grinder to pulverize the whole grains. This will give you a much courser texture. It creates the spaces the mycelium needs to burrow.
I also recommend you do a 1/2-1 inch layer of vermiculite on top of the brown rice mixture. Do this before the steaming/sterilization stage. It will act as a filter. This way only the spores, introduced via needle, enter the growing medium. This also still allows a sufficient air exchange, while still adding a safe guard.
I did not see you flame sterilizing between each jars injection. If I missed that, never mind. If you did not do that, then light a candle when you inoculate. Heat the bottom inch of the needle for a couple seconds between jars, then inject immediately. It will reduce infections drastically.
Then the last two tips. Do you plan on casing? You will really want to do that for the moisture content, and to prevent matting prematurely. I like a vermiculite, or vermiculite and soil mix. Start with pure vermiculite for the casing. Soil requires pasteurization, and that is not so simple.
I highly recommend the Amazon strain of Cubensis. It is the heaviest, fastest, and best high of all I have grown or encountered. Shrooms over a foot long , and two inches long are common place. It also had the best balanced body/head high, and was very fun, intense, and long lasting. This was the same every time, and for everyone who tried them.