Before ordering my tablet, I read in other places on the forum that you had to be very careful when ordering the tablet, and on the order page, uncheck the option to link the tablet to your account, which would stop it from logging into WiFi via passwords saved to your Amazon account.
Upon receiving it, cancel the setup by selecting a password protected WiFi, backing out of entering the password, and clicking on the "Skip setup" option that would then appear. Then, once you're in the OS (still not connected to WiFi), enable developer options and ADB debugging, and use the pm disable commends to set various updater packages to disabled. (Fire Toolbox can help)
Without doing these things, at a minimum, the tablet would try to update itself.