How do i play Ancient Apparition after the laning stage is over?

Ancient Apparition

The laning stage is easy, it bassically consists of leveling Chilling Touch with a good hard stun support like earth shaker and killing fools, however after that i feel like i'm a one trick pony with only my  Ice Blast .

What should i do after laning stage:

Should i split push and just Ice Blast teamfights?

Split pushing dangerous because you're alone and have low HP, very gankable.

Should I be close to the team fight to try and apply Chilling Touch

Be with your team, they need your helpful Ice Vortex debuff too. You can cripple the enemy team so well with it. Chilling Touch is only bad to apply when attacking buildings. They're unaffected by it and you're basically attacking slower for no benefit.

What general skill build do you suggest, i normally go with E>Q>E>W>E>R>E then max W then Q

Ancient Apparition is very flexible. There are max Q/W/E builds that all work nicely on him.

What items would you suggest and in what order, when do I not get Aghanim's Scepter?

As a support, you need to make whatever your team needs. Urn of Shadows,Mekansm , Pipe of Insight, Arcane Boots, Eul's Scepter of Divinity, Force Staff, Rod of Atos, Scythe of Vyse, Shiva's Guard, Aghanim's Scepter. It's all situational, but Aghanim's Scepteris a good staple. It makes your ult last something like 10 seconds longer on enemies so it helps your team out a ton.

Make sure your team has a Mekansm before going Aghanim's Scepter

One of the strongest parts about Ancient Apparition ult is that it nullifies healing. If you have a Mekansm and the other team can't use theirs you are at a huge advantage. Do not Chilling Touch really slow attack speed heroes like early/mid game tiny if you can help it.

Don't ever go solo as Ancient Apparition 

You're squishing than Crystal Maiden's... Okay, that was just cheesey but you get the picture. Stick with your team and toss out your AOE slow/magic buff when fights begin or an enemy hero tries to flee. Your Ice Blast is (purely my opinion) one of the best in the game. It works great at shirt range, it is just a little harder to land. Check youtube for videos of Dendi playing Ancient Apparition. He goes mid and (in the one I watched) absolutely ruins the opposing Storm Spirit.

My usual build for ancient apparition is to get a Magic Wand and Power Treads and then build Eul's Scepter of Divinity's and then Aghanim's Scepter. Super late game you can go Refresher Orb and Eul's Scepter of Divinity and Shiva's Guard. Be sure to buy Observer Ward and Dust of Appearance etc throughout the game.

You can push the lanes when safe to do so (ie all enemies are accounted for and you are close to your towers), otherwise stick closer to your team.  Ancient Apparition is very frail though so positioning yourself so you aren't initiated on so you can't be killed easily in fights is important. I think your skill build is fine although you can max Cold Feet first if you don't have as much magic damage on your team.

Don't underestimate how powerful Ice Vortex and Cold Feet are in the Midgame. 

Cold Feet is the 3rd longest non-ulti stun in the game, after shackle and unstable concoction. If you can drop your Ice Blast and force an important hero to run away for 4 seconds, you've already done more than most supports.

Ice Vortex is one of those spells that no one really appreciates until they sit down and run the numbers to realize "hey that did a ton of damage". Every time you see someone running away with <200HP ask yourself if Ice Vortex was on them when they were hit by your team's magic damage. If they weren't they probably would have been dead. If just a 4 second cooldown and 1500 range, you can just back up and use your downtime after using Cold Feet and Ice Blast to slow people trying to run, catch people in the trees and boost the team's nuke damage. Most supports don't have they luxury. They drop their first load of spells then back up because they can't accomplish anything for 10+ seconds. Ancient Apparition does that too, but he can help finish kills even when he is hiding in the trees.

Your ideal teamfight should be to stand somewhere near your team's initiator, drop Ice Vortex as he blinks in,  Ice Blast whoever he catches so they can't get healed, get close enough to Cold Feet the backup trying to counter initiate, move back, cast another 2 Ice Vortex for vision or bonus damage, if you still have mana try to help a teammate with a second Cold Feet, and get out. If your team did about 1500 nuke damage and you caught 2 people with your  Ice Blast, you just did around 2000 magic damage and prevented another 500 healing from Mekansm while laying out 7.5 seconds of stun and a very sizable amount of slow. If you managed to pull off that kinda of performance on a "teamfight" support like Lich or Earthshaker, you would be yelling about dunk!!!! or OP bounces.