I'm not as familiar with Mint as others, but I think it's just a flavor of Debian (to which Ubuntu is as well). You can log in to your root account by typing
sudo su on the command line. Because your main account is a part of the sudoers group you have the ability to use sudo. If you're a former windows junkie who has seen the light like I was, then it's similar to right-clicking on a program and saying "run as Administrator". As long as you are using your main account and you have a secure password I think you're probably fine.
RE: How to properly setup SSH Key Authentication - If you are logging into your server with root, you are doing it wrong!