Just follow instructions exactly, no shortcuts! And with anything involving CMD prompts unlocking bootloaders etc., be prepared to brick your phone. Samsung does not believe in making this easy anymore. It interferes with profitability.
Okay well it wouldn't be a bezel since a bezel is a physical thing and does not miraculously just appear. It could be that somehow you turned on an accessibility feature like zoom or assistive touch.
You can get Google Play services and playstore installed on fire tablets it's pretty easy really. Just just do a search for it in your browser and download and install 3 files. Takes about 20 minutes depending on download spreads.
I'm just using a Firetablet HD10
It's more than enough to read books watch YouTube and movies. Had to basically do some lite hacking to get it to run Google apps though.
You don't need to pay for it. Just use the basic. It does pretty much what assistant did, although maybe a little more complicated. There is a learning curve.
According to google Sounds like you Gmailify'ed your yahoo email. open the Gmail app, go to Settings, tap on the Gmail account you want to unlink, and then tap Unlink account in the "Linked Account"section