I just attempted this beer over the weekend and I had more than a few hiccups. My first AG brew as well.
I used an entire sheet cake and defatted in an 8 qt. pot. I know full well I didn't defat it very well. I got a decent amount out, but by that point the mashing process had already resulted in two messes and a lot of sweat and tears so I decided to go for broken.
Took forever to cool in an ice bath, which only worried me more about the fat, and in the morning I could see a few globules that all but doomed the thing in my mind, but low and behold somewhere between 7 and 15 hours post-pitch, the airlock is bubbling up a storm.
I'm still worried it will halt early or that I might drain off the residual fat while bottling, but maybe I'll keep getting lucky.