Question [Q] Modifying an Android OS to auto start an application masking all the Andriod UX

Im thinking about ordering a bunch of Android dongles from China, I have an Android app that I want to install on each of those and I want to give that dongles to my clients.

The thing is, my clients are not technical users, I want them just to plug that dongle on their TV and when it power on, my app starts, no android loading/splash screen (I want my own loading animation) and no Android UX (like the lock screen, the lower bar and so), I want the dongle to looks like i was made only for my app.

How can I archived this? Do you know any other solutions like this one? Thanks!