I am happy to see that you are interested in NativeScript. Now, straight to your concerns:
- You can run NativeScript projects in Android emulators. Unfortunately, this is only possible in the AppBuilder Windows client. Here is a link for reference.
- About the Application Package build, could you please elaborate a bit more on the issue you are experiencing? For example, does the build throw an error, or the whole App Package option is disabled on your side? If there is an error, please share it with us.
I hope this helps and I am looking forward to your reply.