Android firmware modification?

Question

Android

The enterprise has Android phones of various brands (2-3 types of devices).
All phones are rooted and all unnecessary applications are rooted out - only the phone, zoiper and standard system utilities are left.
Phones are used as walkie-talkies through the SIP client.
The main problem is that people install the left software and use phones for other purposes (install chrome, sit on VKontakte, etc.).
Actually the main question - how can I sew up a custom launcher, which will roughly speaking have 3-4 buttons and which cannot be closed / unloaded from memory and get access to standard Android?
Or modify the native launcher as much as possible by cutting out all the settings, unnecessary menu items and standard applications.
I will be glad to absolutely all the answers, as well as links to materials for self-study on this issue :)

Answer 1

The file /system/etc/hosts. You write there, say, 127.0.0.1 android.clients.google.com, this is against Google Play. You can cover everything (except company resources).

Answer 2

Or maybe they need to cut off the Internet?

Answer 3

maybe we should look towards the device administration api?