Oh, the writers have done a great job of hinting at all these places being amazing, but just in the corner of our eye, allowing our imaginations to make it something desirable, just out of reach. I worry seeing it might ruin this.

But. Having said that there are 3 places I would love to visit for different reasons.

Sights - Val Royeaux - I so want to see the Cathedral, with the new graphics I hope they can make it as beautiful and stunning as it is described.

Story - Kal Sharok - We hear so much about these dwarves, and how they survived the Blight, but no details, I want to know what happened!

Lore - The Black City - maybe we will finally find out what exactly happened there (I know, I know, unlikely) but come on, I want to wander round the former seat of the Maker. They'd have to do it in an annoying way, a magic shield that protects us from the taint, or maybe we are a grey warden again thus immune to the taint? But I so want to go there.

1) Is blood magic inherently more powerful than any other kind of magic? It seems every mage gets a boost of power if they resort to it, but can a mage be the most powerful without blood magic? And even so, would he be even more powerful if he did?

2) About the old gods of the Tevinter Imperium, they were seven dragon like creatures, correct? But were they alive and free during the height of the empire or they were already buried? Did the action of storming the Golden City affected them somehow or it was only latter when the Darkspawn found them?

3) What is the precise relationship between a bloodmage and a demon? Can blood magic be used without the involvement of demons or that is its very definition?

I guess that's all...

Apologies for the really long post.

1. Blood Magic has 3 elements.

  -  it can strengthen ordinary spells using blood as a power source (as I assume lyrium would strengthen them)

  -  it can cast spells using blood instead of lyrium using blood as a power source

  -  it can do spells only blood magic can cause e.g. mind control.

So I gather in essence it can do special spells, and uses blood to replace lyrium

I guess it is stronger if a mage has no lyrium, otherwise it also grants the use of spells that are otherwise unusable.

In the sense it lets you do more, it is more powerful, but it comes with a price, your blood, or others.

2. Ok, this is the big one with the most contention and really should have a thread of its own.

Yes they were seven dragon like creatures - this we sort of know because when they are awakened by Darkspawn they are dragon like. 

According to the Chantry they were alive but not free, during the reign of Tevinter as they were trapped underground. However they were able to dream, and thus enter the fade, and this is how they communicated to the Magisters. For me the question is why were they underground? Were they trapped by the Maker or something else. (Chantry teaches they used to be free, and then convinced humans to worship them, and the Maker punished them for it by trapping them underground) - was it the maker, or some other being that did it? Are they the evil Gods from the elven pantheon who were trapped away from the world. 

Great conspiracy theories here, again think it should have its own thread.

The Old Gods taught them blood magic according to the founder of the Imperium and encouraged them to enter the Golden City according to Corypheus. I take the currently cannon idea that it was golden, they expected it to be golden but when they got there their presence turned it black. 

There is some debate about whether it was always black due to Corypheus (the high priest of Dumat) saying to Hawk (while delirious and thinking he is talking to Dumat):

"The light. We sought the golden light. You offered... the power of the gods themselves. But it was... black... corrupt. Darkness... ever since. How long?"

I mean I take this to mean it was golden. When you saw it in the fade it was golden. But by entering it became black, and has been ever since, but others disagree. 

Again, this debate could really use its own thread.

3. Demon's know blood magic, how or why, we don't know (which when you think about it is really odd, since they don't have bodies, and thus no blood).

They offer to teach it to mages in exchange for something. Given the Chantry's prohibition on it, there are not many sources for learning about it beyond deamons, but there are some and it is possible. I assume in Tevinter there are books on it. In that sense it is a school of magic like any other.