What happens if I don't have a NY state DMV ID NUmber Client ID Number?
That would mean that the ADM course completion could not be applied to your license record. You may also be required to file a Request for Driver and/or Vehicle Record Information form, before you are allowed to take another ADM course.
Do I get the same benefits completing an I-PIRP course as I would a classroom PIRP course?
Yes, you would receive the same benefits. This includes being able to reduce your driver violation point total by a maximum for 4 points and entitles you to save 10% on your auto liability  and collision insurance premiums.