To add Android O elements to Android Studio 2.3, I had to temporarily switch to the Channel Channel in Android Studio:

Then, in the SDK manager, I could load the O Developer preview items:

... along with 26-rc1 build tools, platform tools, and an emulator:

This should help you overcome your current problems.
This project is corrupted because it refers to @mipmap/ic_launcher , which does not exist. You need to get rid of android:icon="@mipmap/ic_launcher" from the <application> Application/src/main/AndroidManifest.xml element, after which the application will work.
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