[Kindle Fire HDX 7" & 8.9" Q&A, Help & Troubleshoot] Faznx92:
Most of your questions have been answered before but I will try my best to re-answer them. I will try to clear up any misguided understanding you may have.

-Does it update over internet data connection, or just wifi?

+It updates over a internet connection.

-What is the safest build if I want to possibly unlock the bootloader when it is released??

+We don't know yet. Stay on the version you're on for now.

-4. I don't want to mess with safestrap for now, so I will pass on that. Is that OK to do??

+If you don't know much about what it does it's best for you not to worry. Yes, it's fine to leave safestrap alone.

-5. Block OTA updates with #4- Does this still work on the latest, safest build?]

+Yes, it works. The only time it may change up is if Amazon pushes a update with different package names or functions.

-Is there any way to BU (Back-up?) original firmware before installing HDxposed stuff and google apps without safestrap?

+No. I'm not aware of any other way to backup the stock rom.

-Can you just re-install a manual update to recover if things go southafter reversing all the apks, modules, root, etc. after a factory reset?

+You can't re-install a update. You can factory reset it.

-To undo the install of the play store, you just uninstall all of the above and unroot via supersu? And reverse the OTA blocking?

+There is no need to uninstall play store before a factory reset because the reset wipes it out. You should un-root via SuperSU and remove my ota block. (I reset while root but was unsure how safe it was.

It did work out in the end without issue.

)

Keep the wifi off once you undo the ota block and then factory reset so you don't update. Once the reset is done, re-install the blocker. I'm not sure if you need to remove safestrap before a factory reset.

To make clear:

If you install a ota blocker it's good to check that it works by being connected to the net and then going to Settings->Device->System Updates->Check now. If it says Last update failed it is working else it is not.

The current roms for the hdx require Hashcode's safestrap. But to get the rom's working you need a backup of the stock rom or you could use the backup he provided. Once a slot is made you would install the rom zip to the slot.

I believe safestrap works be emulating a new system/data/cache partition in a file as a full rom to the bootloader. I recommend blocking ota before you make a backup or installing a basic stock rom. If you create and install the stock rom to a rom slot without blocking ota, the amazon system files are still in place to call for a update and hand it off to the system and bootloader.

Safestrap is safe as long as you do not touch the stock rom but only to make a backup of it.

If you don't feel comfortable using safestrap then don't.

Quick word of advise, you should include the version of your device when asking questions for that version. I'm guessing your on 13.3.2.4, the current latest.

Also I highly recommend staying on your current version and not moving forward.

Last thing, give this a read.

I hope I answered your questions as clear as possible.

Anybody else please clear up anything I missed.

Also good luck with your device and play safe.