There is no Riften. Riften is on skyrim
In The Elder Scrolls IV: Oblivion, the merchant in this location is called Shady Sam.He sells the player things like lockpicks and poisons.
Have you tried talking to the merchant(hiding) beside the gate to capital city(I forgot name)?
Join the mage guild, get all the recomendations, enter the university in the imperial city, use the spell making alter.
You can buy them from Shady Sam, he is north of the stables outside of the imperial city along the wall. He is there day and night,
Seed-Neeus lives in the city of Chorrol, in northwestern Tamriel. She can be found there at her general store, Northern Goods and Trade.
After the guy has come running to you and you complete the quest by slaying the vampire you should learn that he lives in the imperial city.
The Imperial City Guard shield would go well, and a silver longsword, or ebony longsword.
The Imperial City Waterfront House is available from the Imperial City Commerce Office in the Market District. However to be able to purchase it the disposition of the person there must be 70, I think, or higher. It costs 2000 gold for the house.
There are many Temples in Skyrim, one in each major city.
Right at the end once you've gone through Mankar Camorans paradise and retrieved the Amulet of Kings. Mehrunes Dagon will attack the Imperial City. Wabajack can destroy him instantly for soem reason...
Assuming you mean spell scrolls, both merchants at the Mystic Emporium in the Imperial City Market District sell some. Check the Mages Guild branches in each city, they have scroll selling merchants too.
Unfortunately, no. But the prices for both "Infernal City" and "Lord of Souls" are pretty cheap.