One Hand is a big one. Go with Armsman perks when possible.
Pick the armor of your choice. For a battlemage I'd probably go Light, but either will suit a spellsword. Choose perks that enhance its effectiveness, they will synergize with smithing.
Learn Smithing to produce high-grade armor and weapons, you'll need both.
With Destruction, expect battles to be long-lasting, since you can't boost damage. Any enhancement or defensive potions you use, you'll need multiple ones for each battle. If you're doing the Main Quest, focus of lightning, which is useful against dragons.
Restoration is always useful for keeping you alive. And Alchemy will make you lots of money.