This is a hybrid playstyle, which means all else equal, does neither Magic, nor Melee as well as either specialist. You won't have the Health Pool of the Tank, nor the Magicka pool of an Impact spammer. Therefore, a Spellblade's primary advantage is versatility, which means being mobile enough to transition between mid-close range on his terms. This is why I suggest Light Armor, or Robes with Heavy Armor around it. You aren't a tank, never will be a tank, don't try to be a tank. Remember "A generalist beats any specialist by not playing his game." Stay out of tanks' reach, cut down Archers/Mages with a Critical Charge if you can, but never try to take them in their field. Spellblade is all about avoiding their Strength, while exploiting their weakness. That, and being prepared for Any fight, with proper battle tactics.
Prioritize Archers. Assuming a mixed front of Bows, Meleers, and Magic users (like the Forsworn.) A lot of these battles are set up so the tanks hold you, while the others hang back, and shoot. Archers have greater range, and will try to keep you at the critical distance where they can hit you, but you can't hit them. However, you can run faster forward with spells charged in your hands than they can fall back with an arrow drawn, so close the gap. Mages' priority depends on how much Resistance you've got stacked up. Meleers can be evaded indefinitely, but if there's room to maneuver, I save them for after all the guys that can shoot me while they keep you pinned/surrounded are dead. With both, an effective tactic is to Wuld forward, they typically fall back, either to draw a dagger, or put some distance between you. Critical Charge with the sword, it cuts right through Wards, and Archers are relatively defenseless.
I'd stay with the classic Sword, because it strikes faster, and skip the weapon specific Perks because you have so many to fill. Same with Dual Cast/Impact, keep the sword out, so you can strike any time they get within reach. Dual Wield/Savagery is nice for when you inevitably get mobbed. If you're doing a stripped down (3 skills, probably Destruction/1H/an Armor) build, you might have enough points for Weapon specific perks late in the game, but don't depend on them the first time.
Don't specialize in elements, you're building around versatility, and the main thing Destruction has going for it is the variety of options in combat. Lightning Bolt is a hit-scan, great for Archers, Dragons, and Mages. Flames can be pulsed to stack up On Fire status, and finish them quick, as well as hose multiple enemies at close range (just out of reach.) Ice Storm is just abusive if you know how to use it. Walls of Flame/Frost shouldn't be used like Walls, as such. They have no defensive value, and their 20 second duration is wasted if they run right through it. Try to bottleneck them, and keep them in the fire/rink, or kite them over a road of damage. Runes work as a low level alternative, but only until you can cast Adept level spells with the perk. I get good mileage out of Deep Freeze, and Disintegration only if you aren't using Any Necromancy. Do not get Intense Flames, it's counter-productive.
If you feel like Crafting, Enchant. If you're not going for Free Destruction, fortify Health, Healing Rate, Magicka, and Regeneration. Absorb effects on your sword/s, you can make up the damage from Smithing by hitting them first, then healing with every strike. Absorb Magicka is extremely nice for when your gauge is depleted, and you're using Stamina in the fray. If you have the right slots open, Fortify 1H is a reasonable substitute for FD, and makes up for not Smithing.
_Flesh is an ok way to reinforce your armor, but it puts a real dent in your magicka pool right before you go pick a fight. You might be better off with Flame/Frost Cloak for constant damage on top of your Sword/s, and possibly Stamina drain so they can't Power Attack. You can also run through the fray with a flame/frost cloak to set several on fire, or slow them, and hopefully smack the biggest one on the way by.
http://skyrimcalculator.com/176284 Notice, that's 19 points just in 1h/Destruction. These 2 trees are what eats up half your perks, and are the bare minimum for an effective Spellblade. That's with no Armor, Enchantment, nor Conjuration, right about the time Destruction starts becoming less effective (on Adept.) Any more you add just makes Destruction progressively less effective. I did just those 2 skills with Altmer. The Magicka Boost means you can invest in Health early. Highborn will blast through your Daily Dragon, nothing drains your Stamina except Critical Charges, which are at-will, and you can run faster than most NPCs can Sprint. You have to, though. Even with all level points in Health (and enchantments to fortify Stats) you will be squishy, and vulnerable.