Uh, I'm really not sure how I feel about 'surprise' preps. This literally would allow you to suddenly claim anything is prepped when it was never supposed to be, which could save your character from otherwise certain death in the right scenario. If you can count sudden things as preps simply by aiming them, then this would logically also apply to me.... which I'm sure would lead to us both pulling preps out of our asses any time things look dire for us.

As for speed casting while prepping, I have no issue with this since you said he'd only be able to actively prep a single action.