Do they have to be whole numbers? There's nothing preventing some of the stat increases from the last materia you meld be lost.
That's true. I'm curious if somebody that ends up going PIE+DET on WHM novus ends up requiring less alexandrites and materia... or a BLM going Spell Speed +44 and Critical Hit Rate +31 instead of Spell Speed +44 and Determination +31. Would the amount of alexandrites/materias be different for either BLM scenario?