Default [Q] Beginner Help

Hi all,

I have been an iPhone user for a long time and have become frustrated with the methodical cycling of old tech via new OS', so I want to switch over to Android. That beginning said, I want to upgrade my phone to Cyanogenmod 11 (M5 I believe?) but I definitely need some technical help. I am not looking to brick my phone.

I read a few guides on how one goes about upgrading their device but there are still some points I am unsure of. A large area of confusion for me at the moment is this:

-What is the difference between a unlocked bootloader and a rooted device? My understanding is that an unlocked bootloader is more basic, like having access to the "BIOS" in your phone. A rooted device, on the other hand, pertains to the OS, as if one was upgrading between Ubuntu and Windows. I am confused because the article I read states that I can flash a custom ROM in the unlocked bootloader, without rooting. If this is the case, why would anyone want root access?

-Nightly vs. snaphot vs. stable: I understand that these represent levels of stability that increases from nightly to stable. My question is regarding updating. If I install a nightly/snapshot, will I have to flash/wipe/etc every time I want to install an upgrading nightly?

-Lastly, I have had on my eye on this guide for when I upgrade: (REMOVE BRACKETS FROM "COM")

true-android.blogspot.[com]/2013/12/update-verizon-galaxy-nexus-sch-i515-to_17.html

Is that good guide to go by? Does that make any assumptions about upgrading that new user like me would not be aware of?

Thank you for any help.