Best way to install Android app on 500 tablets? We have 500 tablets that need to go out with our Android app pre-installed. From our experience so far, the only way to install the apps is by creating a new Google account, logging into the play store, and installing the app. The problem with this method is that it's very time consuming, it's creating junk accounts that I'm sure Google doesn't want, and each new account requires a phone number to verify and you can only create a limited number of accounts on a single phone number.

The obvious alternative is to side load the app with the APK file manually, but the downside to this is that we want to be able to update the app later. My understanding is that if we side load the app we can't update the app automatically.

We are already using Ionic Pro which has live deploy which handles most small updates but it can't live deploy any updates that involve updates to the cordova/native plugins.

Since both of these methods have drawbacks, I'm hoping there's another way. I'm curious how educational institutions are able to preload apps on classroom tablets that update without an account logged into the Play Store.

To be clear, and to avoid duplication of other similar questions, what I'm really looking for is to use the Google Play Store for updates, not bypass it, but without having a unique Google account per tablet.
I do not think you need a unique account. I have several devices that all use the same account. That aside...

Sideloaded apps should be able to update from Google Play. I just tested this myself. I installed an older version of Discord on my phone, opened a fresh run of Google Play, and checked for updates. It showed me that there was an update and was able to do it.

Since 2015, Google Play is able to detect the keystore signature of the apps. As long as the one installed and the one on the market are signed the same, then it should update.

You should be able to test it yourself, assuming you have older version of your app that you can fiddle with.