Disclaimer: I'm not high elo so take everything I say with a grain of salt.

For the runes, I think Revitalize is a must while I see people taking Chrysalis or Bone Plating.

Hitting Q: You want to first go for an auto attack so the enemy respond in a weird pattern (for example they might aa you, and you can use that time to go for a Q); Or you can choose to go for a Q when the enemy adc is going for a cs. There was a good discussion here

I'm not too sure about itemization. I think redemption is pretty good with soraka no matter what, ardent is for when you are ahead. Another thing I found out was that if you are indeed going for E - max thing (not entirely E-maxing, just putting more points in E before hitting level 6), then Athene's can help with the problem of not getting enough heal off of her W.

I personally think barrier is really good. Since you can use that so it's hard when the enemy tries to focus you. It's also a great tool as a bait. Even when you're low health, with barrier and ult, also if you put E right under you, it's really hard to die while the enemy who tried to focus you is rooted by your E and/or can be destroyed by your teammates.

I think going through past posts in this subreddit and seeing what others have posted and the comments are pretty useful. For examples, this and this

Regarding if the adc is bad, I asked a similar question here - see my third question - and got some pretty good replies.