So, “traditionally”, dF are used in sets of four. That was my initial baseline for characters in the new game, too. The investment mechanic complicates the normal scale of actions, however, because every die so invested irrevocably lowers the maximum possible roll result by 1. Difficulty scales are going to have to be considered not just for a standard four-die roll, but also factoring in the assumption that characters may be walking around with one or two of their dice invested in keywords, retaining only a portion of their dice to actually make a roll.
I also have to weigh the effects of making the number of dice a trait that can be improved with experience. It seemed like a logical idea, but it may be potentially unbalancing as the current scale is constructed. My instinct is to shy away from that and focus on developing keywords (either gaining more or improving the quality of those already possessed) instead of giving characters more dice. Which, now that I think about it, is derived from me applying Spectrum thinking to this. (No, I haven’t forgotten about Spectrum, but there hasn’t been any development lately due to there only being so much time in the day.)