Here this link should give you all your training needs (check Related Links).
I believe it is Palonirya, who has a Mercantile skill of 80, and the Master trainer for Mercantile also.
Impossible to solve.
The Arena in the Imperial City
No, but you can invest in shops once you get your Mercantile high enough. If you're looking to own a building, you can buy houses by asking counts and countesses of cities.
Not really. Oblivion has a main plot that has to be followed. The events of this plot are part of Skyrim's background. In canon terms, the main character from Oblivion becomes Sheogorath, Daedric Prince of Madness (as portrayed in the Shivering Isles expansion), and indeed, the Sheogorath you meet in Skyrim will hint towards having witnessed the events of the Oblivion Crisis personally, as well as saying his power was given to him.
mercantile
yes it does so if you have a character you like then i wouldn't un-instill and reinstall the game.
Yes, though occasionally the character travels to the Realm of Oblivion, and once to Henantier's Dream World.
the Argonians on oblivion are lizard like.
the best starting character would be a thief born under the thief sign with the assassin class
You don't need to be in a city to level up skills.
you automatically run when you push the stick the whole way forward.