I'll repeat the immortal words of Douglas Adams; "Don't panic."
The switch is going to be a lot easier than it is made out to be. These are all devices that pretty much do the same thing... it's just that they are in a different location. It's like going to a new supermarket after shopping at the same one for years. At first, you feel like you can't find anything and it's a little bit frustrating, but it doesn't take long before you start to find your way.
One thing that I know trips up a lot of former iOS users tends to be the level of customization that Android provides... But just because something can be modified doesn't mean it SHOULD be modified. Get comfortable with the phone, play with the settings, toggles, go exploring menus, etc. Won't take long before you know what you are doing. Worst case you run into a roadblock, but come here and there will be someone here happy to help.
A couple of things that may or may not be in those guides:
Google Play Music will store up to 50K of your songs, free of charge... and the songs are accessible via the Google Play Music app on your phone, or the GPM web site (
https://forums.androidcentral.com/e.../https://play.google.com/music&token=DJZkHPY0). There's no iTunes application, etc. And you can download the Google Play Manager on to your computer and it can take your iTunes library and automatically upload it into Google... that is, if you want to. I have good internet access (mobile or WiFi) pretty much all the time, so having my library there, ready to go, whenever I want is nice.
Second... Google Photos... I can't stress enough how good this service is. Make sure to have your pictures and videos backed (the Google Photos app will allow you do to this VERY easily). And you can also take all your iPhone pics and videos and push them up... it's a great service and it also offers unlimited pictures and video storage (while not in original quality, I can attest that they is as lossless a compression as you'll come across...).
There's a lot more.. but come ask here if you have any questions or issues.