I came across this thread while looking for an answer to the migration problem. I just wanted to say that if you use a separate account for purchasing from the store (personally, I use my husband's account) all you do is sign in to iCloud with your me.com address (if you don't have one you can create one) then go into the Store section in Settings, sign out of your me.com account and sign back in with the account you use for purchases. The options for automatic download of purchases are in the Store section of Settings, not the iCloud section. When you go into the app store, you'll also get the cloud option for downloading purchases made on the Store account.
The use of the same iCloud account on ten different devices would really only be useful for one person using all those devices. So for us, I'm logged into the same iCloud account my iPhone and iPad whereas my husband is logged into his own iCloud account on his iPhone but we can still share the same Store account. I personally don't wat to be getting my husband's messages and emails etc., I'm not that much of a snoop!
In theory even with the same Apple ID each phone is unique and so is every iPhone backup. For example, my wife and I share a few apps, but everything else media and some contacts are different because we wanted different things on our phones, which is natural. So in theory iCloud should only set up and restore what was on that phone to begin with as iTunes does. It's going to ask what backup you want to use.
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The use of the same iCloud account on ten different devices would really only be useful for one person using all those devices. So for us, I'm logged into the same iCloud account my iPhone and iPad whereas my husband is logged into his own iCloud account on his iPhone but we can still share the same Store account. I personally don't wat to be getting my husband's messages and emails etc., I'm not that much of a snoop!