I am a fan of the N de M, but I collect way too much in other roads! The 3rd Rail N de M original scheme was fabulous in the first run. Wish I had been able to swing one of those.
As to minimum numbers for a paint scheme to go, it does vary. Sometimes smaller runs work well to round out a complete run of all road names during any production cycle.
If it weren't for the number of 3rd Rail locomotives and cars I have on order now, I'd join in and get a pair. Might be interesting pulling my "Really Southwest Limited". Chicago to Los Angeles via Hermosillo.
Interestingly, the NdeM Hudsons were called Niagras in Mexico and where the lightest of the class built. Any of the rebuilds out of the San Luis Potosi shops were quite genius and they managed to keep the PAs running longer than any US railroad.