I don't think there's any way to force a single-click cancel, although changing the size of the maintained window is relatively easy. As for the number of icons, yes, we're currently limited to 12 unless SOE decides to add more DynamicData objects for more icons. I really wish they would, whenever I get into large battles with my inquisitor it becomes nearly impossible to remember how many debuffs I've cast, since I'll usually have at least 15 buffs/debuffs going at any given time.
