I guess it's like learning rocket science. You have to start from the beginning and take one bite at a time. But you have a good head start, those ressources you mentionned are those I used myself when I started playing 1 year ago and from them I learned a lot. Searching for specific things in this forum and asking questions is also a good way to get information. Make sure you always use the updated manual (v.2_5_5) though, but keep in mind that most of the existing documentation is about version 1.11.03 or earlier. For the new patch, you need to read the patch notes and overlay them in your mind with the information of the updated manual.
That said, there are many ways to play this game, some just swim on the surface and manage to do most of what must be done to get decent results (or don't, it all depends on talent and vision...) Others dive deep and explore many esoteric aspects of this game. Some play very fast, others ponder and plan every little detail, and both can get very good results... or don't! again, it's all a question of interest and understanding.
For the game engine, I would advise you to start by understanding thoroughly the command structure and the logistics flow, including command and supply ranges. Learn to move your corps (or armies for the Soviets) as teams and not individuals. Which doesn't mean to have all units from one corps stacked together all the time, but keep them grouped in an area corresponding to their assigned frontage. Command range from unit to HQ's, and the supply ranges too all have a great importance. Plan your troops movement taking this into consideration. I know that when playing the Axis against the AI, it is tempting to run all over the place chasing holes in the Soviet lines, but that is the AI... it won't happen against humans, even against weak players.
Learn also rail repair tactics if you play the Axis. Those are important things to grasp to make sure your army stays in the best shape it can be.
As 56ajax said, reading AAR's can give you a lot of info that you won't get anywhere in the documentation.
Maybe you already do, but you also need to understand the basic strategic and tactical principles of warfare, and how they can be applied to WitE. For that, reading of military litterature can help a lot. Myself I am a big fan of Carl Von Clausewitz and have applied many of his teachings to my WitE play.
Anyway, if I have a last advice, it would be to enjoy the learning process in itself. That will ease a lot the learning curve effort and grant a lot of small rewards! :-)
"The closer you get to the meaning, the sooner you'll know that you're dreamin'" -Dio