I have several questions about the actor value Blindness.
First, how do the npcs react to this value? Like if I create a new spell type and choose it to raise the actor value blindness and set it to be percent, will they react more and more as the amount goes up?
Second, what happens if someone casts this spell onto the pc or it gets reflected? While it crash the game, and if so, how do I set this to not be able to get reflected?

I believe Blindness only affects at 100%-- this is what Blind Moth Priests use for their Blindness; and is, I believe, one of only two variables seen in Vanilla (0 or 100)-- I've never noticed a difference with less, but it may work. I don't think it affects the PC At all-- you can easily check with the console, but because the PC is controlled by us, I would assume it does nothing.