Need to cChange Apple ID email due to ISP change

I am finally making the switch from the slowest DSL speed (1.5mpbs - I know...it took 9 hours to download El Capitan!!) to cable (30mpbs). When I setup my Apple ID years ago, I did not think it through and used my DSL ISP email account versus my iCloud email. My email address will change as a result of my ISP change - I will probably use my iCloud email instead of new ISP in case I change ISPs again.

I have found quite a bit of information in communities - some of which makes me nervous to just follow the Apple manual's instructions:

Change your Apple ID

Follow these steps to change the email address that you use as your Apple ID.

1. Sign out of every Apple service and device that uses your Apple ID.
2. Sign in to your Apple ID account page.
3. In the Account section, click Edit. Under your Apple ID, click Change Email Address.
4. Enter the email address you want to use as your Apple ID. A verification code will be sent to your new email address.
5. Enter the verification code from the email into the fields provided and start using your updated Apple ID. Didn't get the email?
6. Sign back in to all Apple services with your new Apple ID.

Many posts indicate people are loosing files, music, etc. I currently have a MacBook Air and an iPhone 5.

If anyone would be kind enough to provide detailed and correct instructions (if different than above) to ensure I don't loose my files, apps, etc. - I would really, really appreciate it! I am very paranoid about loosing my stuff 😮. Thanks in advance!