Respecting to Safari, you can block cookies if you want to. Open Safari, go to Safari menu (on the menu bar) > Preferences > Privacy, and choose "Always" next to "Block cookies". In this menu, you can also remove cookies.
Respecting to Mail, it doesn't mind if you have it in one or a different user: it will be the same, so I don't think that another account will give you a bigger security
If you set Safari to Always block cookies, some web sites won't work. They rely on the stored cookies to connect with you. I tried this and that was the behavior I experienced.
I think the only way to keep Google cookie out is to stay off the Internet. I delete them and by the next day they are back.