Hi im Ex-Platinum II (dropped cause i didn't play the game for nearly a year).
i tried this, and it's really fun and works, the way you spent talents is perfect, i would leave it like that.
i used different runes (movementspeed + straight magicresist and armor, cause i didn't had different ones on my second account).
i built the items the way you did, but it lacked and it didn't seem uptodate to s6, so im gonna try it a bit different, but other than that nice build.

To each their own I guess reguarding the E vs Q but I already gave my reason for it and that's how I played pretty much every game this season but yeah sion works best vs low range or immobile ADC's like how Kog'Maw isnt exactly low range but he has no escape besides whats his supports bringing to get out of your Q before the stun so you can force a CC on yourself that could have been used on your ADC and if you know its coming for sure like seeing Tarics stun coming for example just hit you Q right before it just to get some damage and slow off.

I would differ slightly on your build although it's nice to see others play Sion support. Firstly for reference: Match History.

My points are firstly, max E always, pushing the wave is not that bad if you ward well and there are ways to use the E dmg to not push massivly. Angles are your friend. Also if you max Q you will lack dmg and synergy with your adc if it misses, which it will against good players. The E minion throw is hard to judge and also reduces Armour so it works well with an adc.

Your best best with Sion support is to pair it with a safe adc against a low range adc. I find he works super well with good sivirs as pressure in lane is important for sivir.

Anyway just my 2 cents.

I love playing sion support but there are a few things that really worry me about you build. You have only 5 armor to start bc you traded armor for mana regen, on top of that you go q first which means you will be taking dmg just to attempt to stun off the start. This seems like a sure way to get poked down before you really even see lvl 3. Also you put 4 points in cd which means yes your moves will be up more but also you will be burning through mana fast using the q. The reason most go with the e first is not just because of the early poke dmg, it is also very mana efficient and a more likely hit. If you take the 4 points in cd and put three into expanded mind you will have a larger mana pool and more health regen since you put your points in strength of spirit. This will allow you to put back on armor runes instead of mana regen and make you more affective as a tank in lane and out. Also since you are building pure tank you might want to think of putting your last point of cd into enchanted armor. You will get the most out of that than the 1 point into cd. In your build order to make up the difference in cd just build a glacial shroud first it will give you more armor and the cd you are looking for and is fairly cheap to build and will add to your mana pool to allow you to use your moves freely, or even the kindle gem which will have to cd you are looking for both build into parts of your build. I am not saying your build doesn't work but I hope this helps you.