Android build doesn't work properly

Hi, guys! I've got a foolish question, but I couldn't find the solution. And with respect to the mobile development I'm a beginner. So, some functions of my application don't work properly:

1. The scene that launches first on Android device is not the one I've set to be the first. I have the scene showing the main menu, it is the first in the "Scenes In Build" list (in Build Settings) and has a "0" index.

2. It does not find paths to the streaming assets. I use the Application.streamingAssetsPath function to find them in the way like below:

   path = System.IO.Path.Combine(Application.streamingAssetsPath, "MyFile");

3. Standard UI sprites (using in panels, buttons etc) have a black color. Of course, I will replace them, but I think I should mention it too.

4. Quit button doesn't work.

If I make a build for Windows, everything works fine. I tested the game in Andy emulator and in an Android device, such errors occur in both. Should I have done something with the apk file additionally in Android SDK?