How to migrate your iCloud account
For #1, one thing to remember is your iCloud account is different from your iTunes/App Store account. You should not lose any of your iCloud documents because that is stored in the iCloud account.

Apple's support page describes the procedure here and you should be able to change it back if you like at a later point. But basically, when you change stores, you don't lose your previous purchases but you cannot update them any longer (because you are no longer hooked up to the store you bought it from in the first place). For these reasons, I have two iTunes/App Store accounts so I can switch back and forth to update my software.