I've seen a lot of issues about buying houses from the Jarl of whichever city you are in. I've just arrived in Riften, and want to purchase the house there for my base of operations.

• Firstly, am I correct that you buy the house of the Jarl's Housecarl/servant?
  
• Secondly, do you need as pre-requisite to have defeated your first dragon during the main quest at Whiterun?
  
• Lastly, I've heard about the bug which prevents buying a house if bartering while NOT next to the throne. Any confirmations?

I've only gone so far as to report the dragon attack on Helgen, and have not pursued the main quest any further. Is this part of the reason?