Q: Reformatting Process

Hello All!

I currently have a early 2013 version of the 15-inch Retina MacBook Pro. I have the latest version of OS X and have recently found myself interesting in wiping my system fully. I recently realized that my HD is nearly hitting capacity and I have too many applications that are no longer in use. I'd like to start over, as well, in hopes that my system will be a bit faster/snappier!

I have an external HD and am planning on using the backup function to back up all of my data. However, I have a few questions regarding the process of ensuring that my MacBook is completely wiped and that all files, data, settings, etc. are also wiped with it. I have read quite a few articles out here which are all excellent, and typically point to a centralized answer.

I am wondering however, before starting the process of reformatting - do I need to de-authorize my iTunes account? Also, what about iCloud? Are there any other steps that need to be taken before restarting and holding down those two magic keys to initialize the process? I just want to ensure that I am starting over brand new. Are there any recommend steps that anyone would suggest I take? I have found several articles about this process but most of them are linking back to slightly older OS X versions - are there any changes with OS X El Capitan?

I appreciate any and all feedback that may be given, and also thank you for your time!!