Changing icloud account without losing data, apps etc.

When you delete the account and choose Keep on My iPhone (iPad), contacts, calendars and other synced data will remain on your device. When you sign in with your new ID to create your new account and choose Merge, these will be uploaded to your new account. Synced notes and photo stream photos are exceptions to this, which is why you have to take steps to save them prior to deleting the account.

If you don't have notes turned on in Settings>iCloud, your notes aren't being synced with iCloud and will not be effected by deleting the account as they are stored locally on your device rather than in iCloud. You can confirm this by going to icloud.com and checking Notes there. If you don't see your notes, they aren't in iCloud so you don't need to email them to yourself prior to deleting the account.

Also, if you have multiple devices, you only need to migrate the data to your new account on the first device. On the second device you can just delete the existing account and choose Delete from My iPhone (iPad) rather than Keep (since your iCloud data is already in the new account). When you sign into the new account on the second device your iCloud data will download to it.

You can migrate your device to a new account and continue to share the same iTunes account. The ID you use for iTunes does not need to be the same as your iCloud ID.

To migrate to a new account, start by saving any photo stream photos that you want to keep to your camera roll (unless already there) by opening your my photo stream album, tapping Select, tapping the photos, tap the share icon (box with upward facing arrow), then tapping Save to Camera Roll. If you are syncing notes with iCloud that you want to keep, you'll need to open each of your notes and email them to yourself so you can later copy and paste the text into new notes created in your new account. Then go to Settings>iCloud, tap Delete Account (which only deletes it from this device, not from iCloud; this will not effect devices still using the existing account), provide the password to turn of Find My iDevice and choose Keep on My iDevice when prompted . Then sign back in with a dif erent Apple ID to create your new account and choose Merge to upload your data to the new account.

You're welcome. To answer your questions...

If you have a Mac that is signed into your iCloud account, it would be possible to set up both accounts on it, then simply drag and drop the notes between accounts. Othwise you unfortunately have to recreate them one by one.

Your apps and other iTunes purchases will be uneffected by this as you can keep the existing iTunes ID even though you are changing the iCloud ID. The IDs do not need to be the same. You will also continue to be able to download existing purchases from iCloud as this service is "iTunes in the Cloud" which bears no connection to your iCloud ID (it's only tied to your iTunes ID). The best course of action is to simply leave your iTunes ID as it is and set up your new iCloud account with a separate ID.