Ok so if we have a reproducible crash on our hands then may I request you to upload the crashing CRE file (before any edits that fixed the crash) and all of its equipped items' ITM files please?
I've got a Big World Project install that also crashes as soon as Tethtoril appears, and can confirm that this is fixed by editing the shield he is carrying.
Here are his related CRE and ITM files for you to take a look at.
All I did was change the shield's "Equipped Appearance" attribute to "D3 - Medium Shield" and now the game works fine, even though Tethtoril himself looks a little odd, running around with a shield!
I've attached my WeiDU.log and a change-log file that I created on the SHLD04.ITM as well, and it does look to me like it's Item Revisions that is somehow causing this problem.
Thanks for all your tips in helping fix this issue!