How is your OS implemented on android?

Question

Android

Perhaps the question is not quite right, I apologize in advance.
The task is to implement your android with the necessary pre-installed applications and limited functionality. Like how online cash registers do on android, but with their own firmware.
So, who are these people who are engaged in such development? What stack should you have?
These are not android app developers.

Answer 1

Yes, they are slightly different people. They most often grow out of embedded. But in your case it is not necessary, I think.
In your case, a person who understands the android framework and knows how to assemble AOSP will be enough. I think I will not be mistaken if I say that many experienced application developers can do this.
Besides, you probably do not want to write firmware from scratch? The most logical way was to get the source codes from your iron supplier and then continue to finish their firmware to suit your needs.