Create a new Unity Project and switch it to the Android Build Target - See here https://docs.vrchat.com/docs/setting-up-unity-for-creating-quest-content
(A completely new project just reduces the chance of something erroring and you needing to hunt down what caused it)

For the atlased texture, scale your existing ones to fit, the main are 1000x1000 and eyes are 256x256. 
For the materials you must use the shaders in VRC/Mobile, the example uses Standard Lite

The example uses a blank animator override, I do this so I don't have to keep the gesture config synced up between my PC and Quest versions, especially if I am using it as a fallback. I'd rather have the Quest not gesture, then make the wrong one at people. 

You should be able to and upload the avatar to Android, you tag it as a fallback on the screen where you set it's name. 