How to dual wield weapons

No there is not.

The only way to block/parry attacks, is to have either only one weapon, or a weapon and a shield, and then press (and hold) right mouse button.

Magic is pretty diverse. Need to kill a bandit? Shoot fire from your hands. Enemy immune to fire? Shoot lighting or ice. Mobbed by a pack of wolves? Charm or frenzy them. Archers hitting you hard? Shield or conjure armor and regenerate health. Need to escape? chameleon or invisibility and paralyze.

But what if you're facing a breton with dragonskin and some kind of crazy 90% magic resist buff? Well, summon up a skeletal warroir, go chameleon, and heal your summon, while it wails on the poor breton who probably skimped on physical armor to get such awesome magic armor.

In short, you don't have to diversify your skills outside of magicka to have a diverse set of combat options.