My first thought is that those are pretty damned small brigades, if it takes that many to make up that number of troops. Of course you're right about never warning an enemy, but I always suspect disinformation when I see announcements like this. It would be unthinkable to try to recapture Mosul using nothing but local forces.
I am sure a good part of the hundred M-1 tanks, 18 self-propelled 155mm. howitzers, three dozen or so Bradley fighting vehicles, etc. that are on the way to that theater would support local infantry in any campaign to retake Mosul. M-1's are pretty much invulnerable in urban fighting--provided they have infantry to protect their rear, where the armor is thinner. A strong force of local infantry on foot and in armed vehicles would neutralize that threat. Continual real-time reconnaissance from drones overhead would also be a big tactical advantage in an assault on Mosul. (So would informers in the city that special forces had previously recruited.)
It might be well, too, to remind the inhabitants of Mosul that the U.S. has even bigger hammers available than tanks, and that it would not hesitate to use them even if it killed some civilians. I'm sure it would be a comfort to any ground commander to have a half-dozen B-52's and B-1's circling safely 35,000 feet overhead, each one loaded with twenty tons or more of guided bombs. For example, jihadist forces trying to assemble or train on the city soccer field might find it disruptive to have the whole field and stadium plastered with a couple dozen large bombs.
I'm assuming all Mosul's electric, gas, water, telephone, and sewer services, its trucks, its warehouses, its radio facilities, its fuel tanks, its roads, wharves, and bridges, and any rail lines or airports would be destroyed in the weeks before any assault. It's usually possible to put these things out of commission only temporarily, so that no enormous cost is incurred to reconstruct them later.
