Keep in mind when I say Russian roulette, there is a good chance that you'll be fine. Depending on how much bacteria was present after cooking, how quickly the rice was refrigerated, how much oxygen it has, etc., it could easily not tip over into problem territory. However, if you're doing it five days a week every week, there's a good chance that at some point you'll lose the game.

If you refrigerate right away in sealed containers without a lot of extra oxygen, you're doing a lot to prevent bacteria from spreading. Soy sauce is a natural preservative due to its salinity and acidity, so yeah, it'll help, too. The bottom line is that cooking rice won't kill all of the bacterial spores that cause the problem, and those spores will start to proliferate as soon as you stop cooking the rice, so best to get everything in sealed containers and in the fridge right away if you intend to make meals ahead of time.