beams and multi cannons is a great combo. If you're having trouble hitting the target though, you may want to try gimballed instead of fixed. Fixed pack a bigger punch, but if you're like me and have trouble hitting the target.... it doesn't really matter how hard the weapon hits.
The Cobra is a great multi-roll ship. As Tor mentioned, the 'next level up' multi-roll ship is the Asp X. The Cobra is great at running missions, carrying a good amount of cargo, and pretty solid in combat. I'd recommend sticking with it for a while as you build your bank account and upgrade the Cobra's capabilities.