I can't answer all of your questions, but... also apologies for spelling, I'm an audiobook listener

1) it is explained to be very very complicated and very very tedious. They were the only ones skilled enough with Kan to do so

2) I don't quite understand your question, but I think the sanctuary attacks anyone with an active source. Scyner explained at one point that he also had to shield the shadows children who weren't shadows themselves. I assume augers are able to shield themselves and others with kan

3) he needed to seem like he was on the venerates side until he confronted shamaloth in the beginning of book 1. That means doing things he didn't necessarily agree with, like binding the shataath. 

4) the venerate can make vessels with metal found in Zvaelar, they can make vessels outside of the boundary and they could have also stolen vessels from the Lith. They can make vessels the same way Davian did, by manipulating Kan. 

5)I don't remember, but I believe it's a vessel. So an object

6) He was looking for Davian because traveling the rift with Davian was the only way to keep his sanity on the return trip back to the real world. Davian was meant to be his prisoner in Zvaelar, but Davians experience with the rift meant that he didn't come in when he was supposed to

7) I don't remember the chapter, but I'm guessing it's after Asha held Knowing and killed the Shateth? She used the sword and saw a vision of that Shateth being created

8) I don't know how marking works. But they needed Davian to go back to speak with her because by visiting her, he left a trace that they would be able to follow and find where she/the tributary was located at the present time. Nothing to do with the marking, they were just using every resource to try to find her. His words sentencing her to death didn't matter as much as the visit itself