Don't use RaycastHit hit = new RaycastHit(); when capturing the touch - that's from code I'd copied for the example.

See the CameraDeviceMenu.cs script which comes with the samples for examples of how to access the camera and also draw GUI elements on screen.

To trigger a focus operation use ...
CameraDevice.Instance.SetFocusMode(CameraDevice.FocusMode.FOCUS_MODE_TRIGGERAUTO);

To close the application use ...
Application.Quit();

e.g.

OnGUI(){

  if( GUILayout.Button("exit") )
      Application.Quit();
}

To catch touch events you can try ..

using UnityEngine;
using System.Collections;
using System.Collections.Generic;

public class OnTouchDown : MonoBehaviour
{
    void Update () {
        
        RaycastHit hit = new RaycastHit();
        for (int i = 0; i < Input.touchCount; ++i) {
            if (Input.GetTouch(i).phase.Equals(TouchPhase.Began)) {
              CameraDevice.Instance.SetFocusMode(CameraDevice.FocusMode.FOCUS_MODE_TRIGGERAUTO);

           }
       }
    }
}

To install on SD memory, add the installLocation attribute to your Android Manifest.

<manifest
    xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.qualcomm.QCARUnityPlayer"
    android:versionCode="1"
    android:versionName="1.0"
    android:installLocation="auto" 
    >

You can find AndroidManifest.xml in /Plugins/Android in your Unity Project panel. This will give you the option to transfer the APK to external storage.