That article describes my method rather well, with one exception. I do not uncheck Contacts in my primary iCloud account. My wife and I want to have our own separate contacts, so I keep mine checked. Then in the contacts app both accounts show up.
I think you already answered your question about the iPhones and iPads, but here is my answer anyway. No they do not automatically propagate. You must set them up on each device in a similar way as you did on the computer.
The key factor here is MAKE SURE you set your iCloud account up first on each your computers and devices. Then, set up the auxiliary accounts. By doing that, your primary account has all of the other iCloud features that a secondary account does not have. Also, you want to avoid the 90 day warning.