To keep the brake temp at max 100°C with help of the brake fan makes no sense from my point of view. 100°C is definitly not the optimum temperature for carbon brakes.
Brake Fans are said to "halve the indicated brake temp" i.e. if brake fans are on, and the temp says 100°C, the actual brake temp is ~200°C and the temp will rise towards this if the fans are turned off, hence why the takeoff limit is 300°C Fans Off, and 150°C Fans on. So working to Fans on >100°C taxying out works well to keep well clear of the 150°C limit etc. We have the 100°C SOP taxy out, taxy in not so...
100°C is not the optimum temp as you, ~500°C is, but for brake wear purposes. The 300°C / 100°C limit is for the RTO case - a max weight / V1 RTO needs the brakes <300°C so they can absorb the energy, if the brakes are already at 500°C they may not absorb the energy required...