BRM works two ways, when to move up, and when to move down. 100 buyins seems excessive to me at microstakes, but comfort level is important. I prefer a much more aggressive BRM approach, but I combine that with strict movedown points as well. At the end of the day, its important to come up with the plan that works for you, and then to be sure it really works for you, and isn't what you want it to be.