I think most of these could work to a greater or lesser extent. As far as buildings go, the covenant is in the ruins of a greek (/roman client) settlement (although so far nothing about the remaining buildings has struck us - we haven't really been looking, though), and there is a local necropolis which did have some tombs with odd features linked to architecture.
Note that there's a three year wait in the charter before a visitor can become a magus, and the saga has so far been fairly slow paced (so depending on your definition, it wouldn't become "his" covenant for a while).
The locals are Kipchaks, yes. There's a bit on them in this post: Covenant
I think the main trade goods down the Don are furs and slaves.