If you're buying the M.2, get an Intel 660p 2TB. Sure, its performance degrades as you fill it, but it can be your primary editing drive.
As for your 2TB question, why so small? Enterprise grade Nearline 4TB's are only $100 and you could go bigger for that price in the client space.
https://www.amazon.com/Inch-Cache-Enterprise-Drive-WD4000FYYZ/dp/B0090UEQ8I