You need a software based firewall regardless the type of computer, or where you use it. And the good news is, W8 already includes the fully capable Windows Firewall and a fully capable anti-malware solution with Windows Defender (a revamped version of Microsoft Security Essentials).
But regardless your anti-malware solution, you should have a secondary anti-malware program handy just to ensure you, or your primary anti-malware program didn't let something slip by and I agree that Malwarebytes Anti-Malware is an excellent choice for that.
As far as an admin account, yeah, W8 has one by default. Got a link to where you read that?