Parry tilt sounds like it would be too slow for a guaranteed punish unless you do parry djl, which I have never seen anyone utilize (but I'm planning to learn it eventually on controller...?) If I got a parry I would probably just djc fair moving forward, which would reach any amount of fade away. He *might* be able to land and shield in time, but that's obviously still bad for him. I guess he could get away with his frame 1 invincible up-B... ****ing Pikachu. That's something almost nobody would do in that situation though (I just know... I know how the community plays as a whole. lol)
IDK the spacing is hard to describe in words. It is true directly challenging Pika's aerials with yours is probably not a good idea. You have to, like, try to stay out of Pika's range when he is in a position to attack you, then go in when he is transitioning into a more vulnerable state (like I said, I like to threaten him when he is landing...)
Fair I think has ~equal range, but I think it might have slightly less "priority" (basically meaning it's less disjointed). But if that's true it doesn't feel like a big deal to me because you will be losing in the disjointed game anyways. In other words, out-reaching his hitboxes with your aerials is not how you're gonna be getting your first hits in this MU, so eh, I prefer fair for the higher punishment.