[Fire HD 8 and HD 10 Android Development] LordUnderling:
Although I may be brand new to the Amazon Fire HD, I've been to XDA before and have had experience installing LineageOS on both a Motorola android phone and a Samsung android tablet so I'm not a total novice.

I've been able to get some things done but do have questions about how to proceed further. Unfortunately, I didn't make any notes and am typing most of this from memory. MY apologies if this appears to be too lengthy.

Anyway, I've just bought an Amazon Fire HD 8 2022 tablet with ads without preregistering the tablet and have yet to register it.

I kept it offline but I did sideload F-Droid using a USB-C device that allowed me to mount a USB memory stick.

(HDMI doesn't work so far so I can't yet display on my 4K TV what's on the tablet screen. I don't know if the tablet is incapable of doing this or if I'll need to go into the tablet settings to enable this feature somewhere.)

The FireOS Version was and still is 8.3.1.1

(I now cannot bring up the version number on the tablet and need to use FTB to find out.)

Using F-Droid, I've installed some open-source apps but not before I connected the Fire HD 8 to a Windows 10 PC running Fire Toolbox v30.1 and successfully killed the lockscreen advertising and over-the-air updating. I did not go online until after doing this and only then did I use F-Droid to download apps. I've yet to install Google Play.

(I now have several web browsers, an offline map and some app launchers but not one that can be the tablet's default. Go to https://f-droid.org/ if you want to learn more about that.)

Linux is my preferred OS but I installed Fire Toolbox V30.1 on a Windows 10 PC that I've pulled out of mothballs. This PC has been kept offline preventing my use of all of the FTB features.

Being completely offline, both tablet and PC running FTB, I was able disable advertising and OTA updating but I still have the stock Amazon app launcher and could not install Google Play services.

Here are a list of apps that I could disable and a second list of apps that I couldn't using Manage Amazon Apps within FTB:

Removed: Amazon Alexa, Amazon Kids, Amazon Music, Amazon Newsstand, Amazon Prime Video, Amazon Youtube, Audible, Device Dashboard, Device Setup, Goodreads, Help, IMBd TV, Mayday Sharing, Music, Prime Photos, Shop Amazon, Weather, WPS Office

Can't Remove: Washington Post, News, My Videos, Mopria Print Sevice, Kindle Store

Next up when I do have further free time is to connect the Fire HD 8 to the Windows 10 PC running Fire Toolbox while the PC is ONLINE to be able to use all of the FTB features.

First question: Should I now register the tablet? Is it now safe from advertising and OTA updates?

F-Droid makes available a some app launchers. Might I be able to use one of these as the default using Fire Toolbox and killing the stock Amazon app launcher?

While installing LineageOS on other phones and tablets, I've installed Open GApps with a minimized Google Play footprint by using either the micro or nano configuration. Can I use Open GApps to roll my own version of Google Play or must I use the version that's made available with Fire Toolbox?

(To the uninitiated, this comes as a zip file that must be loaded by a recovery app within recovery mode but not as an apk file that can be sideloaded using adb. As is known here, this can't be done on the Fire HD 8 2022 at this moment because the bootloader is locked. So I understand that there will be no replacement recovery or LineageOS for the near future if at all.)