I wouldn't bother with an anti-virus program either. But the first thing you want to do after logging in is go to the Safari (web browser) preferences and disable the "Open safe files after downloading" checkbox. That prevents applications that are disguised as images or documents from auto-starting.
So, you don't need steps 1, 2, or 4, and 3 is done with "Software Update", which will run automatically, or you can do it from the "Apple" menu.
Also, if you have anyone else using the computer who can't be trusted to follow safe internet practices (don't open things you aren't sure about), make sure you set up a non-admin account for them to use. And don't let them use your default account (the first one set up on the machine), as it will have admin privileges. Well, they'd still need to know your password, but just to be safe.
joe