Let's break your questions into bits and pieces from the perspective of a self-taught GDL scripter, shall we!!
1. Learning GDL is not that difficult, but you will need guidance at least to least to prevent you from derailing in the wrong way of doing things (luckily enough it's easy
2. MEP although it's GDL, there is a hidden magic of troll fairies at many corners
, just kidding ... If you're going to start learning GDL just avoid MEP for the time being, instead see if you can get your hand on "Library Part Maker"
to make your MEP objects.
3. The aim to learn to GDL is not in modelling in itself, but how to optimise your resources and make you work smarter not harder ... But this takes time (fortunately not that much
), and right now the community is bigger than ever and most important interconnected
4. About modeling in 2D and 3D to create library objects then adding modification parameters, actually it's one of the legitimate ways to quickly create GDLs, as it gives you an insight on how GDL works, and though it's quick method and can work fine, it will never create the best possible results in more than 90% of the times, since that the process of creating parametric GDL objects needs a trait that human excel at which is pattern recognition, but it could be a very good cheat just to get along.