An FAA CPL can easily be converted (convalidacion) to a Mexican DGAC CPL, I did it without having to do a single hour of ground school or written test, it's mostly paperwork, you need your documents notarized, and have them stamped by with the "apostille" and some other misc stuff, it costs a total of about $500.00 dollars for the official part.
Keep in mind . . . the rules clearly state that to be a CPL in Mexico you have to be Mexican by birth AND NOT have acquired any other nationality, so be careful there.
I have a friend and she just went thru the whole process in about 3 weeks and only took the check-ride, with a fixed wing pilot examiner who just wanted a ride in helicopter.
As for the IFR, it's always a nice thing to have but not a must, most guys around here don't have it, but it will help you expand if you have it.
I fly an A109E and 2 guys that I fly with don't have any IFR experience whatsoever, nor do they have the rating, at least around Mexico City it's almost impossible to fly IFR legally since it's so high, to depart MMMX, your airway MOCA's are at least 14,000 feet.
Here is a pic I took a couple days ago here in Mexico City!
