The amount of weapons sold should directly influence the amount of enemies with such weapons spawned. AKA you sell that many daggers, stuffloads of highwaymen with daggers around.
As a proportion - not directly. They would maintain difficulty, just use daggers. Maybe some sold items would end up on enemies you kill?
The status of your character should affect the way people talk to you.
"Go farm some wheat."
"I'M THE FREAKIN' ARCH-MAGE OF THE ENTIRE UNIVERSE"
"Whatever, go chops some wood, kthx."
I totally agree with these. Whatever the player does should affect the world around them, sell stufftons of armor and weapons, prices go down and more people wear that specific set of armor or use that specific weapon out and around the city of sale.
And if you are a Thane of Solitude, you should be able to have like, feasts or something with the Jarl.
One interesting mod in the workshop is trying to create some sort of economy in Skyrim, "Skyrim Trade Guild" or something.