you are partially right. Google is not going to penalize subdomains they are simply going to treat them the same as a subfolder. So it doesn`t really matter how you want to structure your site now. Just think about what`s best for your users and make sure you have a sitemap so that all of your pages are able to be found in one place so the spiders can index them. If you do this you won`t have any issues with Google.