1 guy.
No doubt the administrative hearing can be reduced to something pretty much like an application review, and for enough money I could run 800 a month.
With 12,000,000 people a mere 1,000 examiners could process all of them in 15 months.
Certainly America does not want for qualified lawyers to handle this ~ must be at least that many exceedingly well trained Indian and Pakistani immigration lawyers in this country ~ just "insource/outsource" the job.
When have you ever known a public employee to do anything efficiently? Just asking.