You really need at least one alternate (from a different company!), even though that reduces security. 2 is still better than 150. I'm surprised that Google would accept a one hash pin, but I guess they'll let you shoot your own foot off if you want to.
The other side of that is you must actually be able to issue certs from that other CA. If you have to wait for your account to get set up and verified, you've lost.
