Regarding Solas catching onto Mihris' lie... couple possibilities, here. One is that Solas is just super good at reading people. Granted, he doesn't read Blackwall very well, or maybe figures that as long as he's helping the Inquisition (like himself) it doesn't matter. Also, plot armor. I love Bioware, but they have been guilty of using it.
Or - Solas could have been, in his wanderings, in tune with some events. Enough to investigate them after he awoke, maybe? I would think a Dalish clan imprisoning one of his old acquaintances (if he really did once walk among the Forgotten Ones) and his subsequent bloody release would be something he'd look into. Assuming he isn't somehow involved with Felassan... I'm not convinced Solas was the one at the end but that doesn't discount him being involved with or at least aware of that person. Thing. Whatever it was, and it's plans.
Hmmm... the fact that Imshael also doesn't recognize Solas (as Cory doesn't - though I'm going with the theory that Solas and Cory never actually physically met) does make me wonder if Solas is Fen'Harel in the physical sense. Though it could be that Fen'Harel's travels into the void had him taking on some other, more spiritual, form... Gah, I just don't know 
That PW tweet makes me think Solas is able to conceal things from even other powerful spirits. He may be able to block them from recognizing that he's more than he appears to be.
As for Uthenera, it sounds to me like more of a stasis than normal dreaming where you're aware of things in the Fade.
I was reading World of Thedas and the song Suledin (Endure) reminds me of Solas and his lonely quest. Wisdom tells him "mala suledin nadas"- "now you must endure," and he repeats it. The words also remind me of Lavellan searching for him.
Noticed as well that solas is translated as either pride or "stand tall."
It is a web series. Look up Dragon Age: Redemption. But as was mentioned, it is of questionable canon as the lore is off in places. And its a bit...painful to watch. They meant well, but. It just wasn't my thing.
As far as Solas is concerned- the plot involves a struggle to acquire an ancient relic mask, which had ties to Fen'Harel. I can't remember what the kossith's end goal was in getting the mask, or even if he ever stated it. It just sort of meanders a bit.
He wants to break open the Fade because he's angry about how he was treated as a Qunari mage, so he steals the Mask of Fen'Harel which some Dalish clan had stashed in the back of an aravel, and tries to do a ritual where he sacrifices a Dalish maiden on an altar to Fen'Harel while the mask is hovering over it. Yeah, it doesn't make a lot of sense. I think Gaider should have consulted more closely than he apparently did.