I did actually read through the documentation and FAQ after I reached the informants part of the quest because I was a bit worried that I hadn't run into Julan yet.
When I read through it though, I got to this line:
It is NOT playable by characters who are past the Vivec Informants point in the main quest.
I assumed that something happened around this point in the quest that triggered a meeting with the character later on, or something similar, which meant you couldn't load this mod after you'd reached this part of the quest. I didn't realise you needed to meet him before that point in the quest.
I'm guessing the main reason I'm the first one to get this problem, is that maybe I'm the first one to try and load it up without any prior main quest experience. Had I known that you weren't directed to Ghostgate till the very end of the quest, I would have put two and two together and realised that the run in with Julan wasn't something I'd just come across playing through.
I'll play through if I ever make a new character to beat the main quest, though.