Welcome to my Obsession, Rasnell
The above covers your questions very well. I certainly agree with the ABN missions being really a hard place to start, although yes they are interesting.
The only thing I would add is the "A" All move feature is a fickle mistress, it moves your unit only generally where you want them. Only use when well out of sight of the enemy, and never when there is an air threat, it leaves units bunched up and perfect targets for Jabos!!
Enjoy the game, remember every loss is knowledge gained
Bob out