Works up to a point
Let me say first that video is absolutely flawless, it is very well made and informative and it is easy to see what you're doing. I also subscribed. I followed it to the letter and got the same results as you up to the point where you had adb folder with the new entries in it. The problem now is that the sd card in my kindle will not load. I can use Super ADB Tool to place zips on the card with no problem, and in the command prompt I see it as a device in recovery.
1.But issuing the next command to flash the twrp recovery.img it hangs up, saying "waiting for device". The sd card won't mount in recovery and the dialog box you see doesn't come up for mine.
2.When I do place zips on the sd card and then try to flash them I will get the error message "e:mount: unable to find partition for path '/\sdcard\()\update.zip kindle fire".
3. Connecting with a usb cable, the Kindle doesn't appear as the usual removable device G: drive, it doesn't appear at all as a drive, even though it appears as a device connected to the computer. So the problem now appears to be with the sd card itself I guess.