I've been in the beta for awhile now. I've always exported as cordova. Steps I use:
1. Export as cordova. Default settings are fine.
2. Delete the "config.xml" file in the export folders.
3. Create a folder named "www" inside the export folder, and move all other files and folders inside it.
4. Zip the export folder up as a zip file. Don't use anything else, like 7z or rar.
5. We used to have to delete the default 'whitelist' plugin. IIRC, you don't have to anymore.
6. If build fails, you should get an email with the build errors. Not all cordova plugs work; start the process of elimination.
Don't know about AdMob, I haven't integrated it in any of my projects yet.