Personal curiosity primarily.   It is not as if Hades mentioned much that would not have been obvious in the moment or afterwards.   I think Hades just wanted to meet Harry - a person who he clearly feels some kinship of spirit. 

Got to remember, these gods are people as well as beings of power - especially those greek gods. 

I think Marcone uses Harry, but does not manipulate Harry.   If he got Harry to do things he otherwise would not do, then you have a case for manipulation.   But mostly Marcone sees Harry as a useful club against his own personal enemies.   It is that "I use my enemy to destroy my greater enemy" vibe.

Now I totally realize that Marcone gets supernatural and criminal street cred for "using" Dresden to destroy his enemies. 

And realistically, Harry is not an enemy of Marcone.   Harry is, at best, a potential enemy IF and ONLY IF Marcone chooses to go down certain paths.   So long as Marcone avoids these paths (ie - dark supernatural stuff or lots of direct harm to innocents), Harry is not going to attack Marcone's interests.   And Marcone is not so petty as to resent Harry's strength when it does not come at his expense.     Harry can be an accidental threat in that his behavior can create a PR problem for Marcone, but Marcone has proven apt in navigating that hazard.   

Optimum time to oppose corpsetaker and/or otherwise succeed in what you can do.    Uriel can see probabilities, so he would make sure Harry returned with the best chance of a best outcome.   I suspect the timing was not completely under uriel's choice though -- I believe uriel had to work within the constraints of the "laws of magical physics". 

A bigger question for me is more general.  How did Morgan keep tabs on Harry?     Is it something so simple as checking him out for black magic taint every once in a while and keeping an eye out for supernatural/magic like murders?   Of did he use magic to track Harry.

However he did it, he did not identify that Harry had Bob the skull.

Harry has samples of Molly's hair and stuff from his days of training her.  Sarissa no doubt bled on the island as did molly - as did Maeve and Lilly.   

So if the island was keeping samples, they have enough samples no matter how you run things to have some power of the Summer and Winter Ladies. 

Not sure demonreach did though - it is not its purpose.

And the ladies are too weak as imortals run to have much impact on demonreach.  That island was meant to contain far stronger gods than the ladies. 

I think there might be only two real requriements to get the winter mantle.
1) A queen who is holding the mantle's power decides to make you the winter knight
2) you accept.   

My guess is that Lilly was tricked into accepting, but acceptance was pretty darn important to Mab which implies it is a critical step. 

The only certainties are: 
It cannot require killing the old knight -- as knights die in battle
It cannot require sex as the ladies cannot engage in sex, but can clearly can create knights
It does not require physical presence as harry became the night while his body physically resided in the church
It does require the action of a queen
The night must be mortal (guess, but believe it is solid)

Or alternatively, is that spilled blood available to Harry.   I am certain Harry would gain great power over an immortal if he has that immortal's blood to play with.

Harry is a reincarnated Merlin, still "in process" of building Demonreach.   Reincarnation is what allows Merlin to create Demonreach at multiple points of time.  Harry (this version of Merlin) will complete demonreach stage 2 during the final trilogy.