Hi Allar,
thanks for the elaborate answers. The explanation for prefixes and suffices makes sense, so I will stick to them. 
Another thing I noticed today, starting to work with Substance Designer & Painter: There is a suffix missing for metallic texture maps. Since _M is already taken, what suffix would you give it?
The epic guidelines use _MT. Speaking of which, I am interested in why you decided to use different prefixes and suffixes than epic.
Cheers
Michael