When you try to add the Google account, are you selecting "Google Account" or "Outlook Account". It sounds like you are selecting the latter, which is why it's asking for the server name. Add a Google Account and it should just ask for the account name and password.
There is no advantage in manually setting up a Gmail account as an Outlook account in the WP8 mail app. You end up with exactly the same experience. Just select to add a Gmail account - it does the same thing only the server settings are done for you.