Sorry, I edited my original post for the reply. It said: "I plan on signing up for the following 5 cards soon (already did amex plat (100k) – and aa plat (75k) earlier this year - 4 months ago)"
I didn't cancel my amex plat. b/c when I called to cancel the rep gave me a mussar shmooze about how I already cashed in on a few hundred thousand points (I did a bunch of referrals) and that they like me as a customer....yada...yada. He also offered me another 25k to not cancel.
I took the bait.
So no churning for now.
Also, since I don't have any other amex cards as of now I assume that if I cancel I forfeit any warranty benefits from the purchases with my platinum.
I am hoping that once I have the gold I can cancel plat and still have the rights to a warranty claim from Platinum days.