1) Yes. (and the answers won't get any shorter :wacko
2) Well, there is a manual coming with the game but if you want to learn the game from the manual, this one will definatly not be enough.
There is also the manual for the boardgame on which this game is based (link available in a sticky post above), to a level of detail with respect to the 'internal' rules, that it is way beyond the level of detail you (and me as computer gamers) should be bothered.
As PhilT said, there is a comprehensive manual underway, so if this is what you are looking for you might just wait a little longer.
I did not know/play the boardgame but I think I can handle most of the the basics fairly well against the AI, just by the existing manuals (which I didn't study in all their details....) and actually playing. No doubt so far I missed quite some details (never bothered about my generals :rolleyes

, but it is certainly enough to get familiar with the game mechanics.
3) This game has less than half the number of turns and the units you manage are much bigger (corps here vs. brigades in AACW). Yet, seeing the division of the turns in multiple phases, the amount of soldiers involved in this conflict compared to the AACW spread over multiple fronts, along with the diplomatics I think the overall complexity might be about the same, but with some new aspects.
4) Haven't tried 1.0.4e yet, but the latest patches brought a significant improvement in stability (as in no more crashes).
However, there are still some gameplay problems that (at least for me) are rather serious. But while they might prevent me from steamrolling the AI, I am still able to get used to the overall gameplay and also get some fun (not so much in slapstick but more in excitement) moments.
But you can wait for the 'anniversary' of the Versaille Treaty - wasn't this meant to be the release date anyway?!
5) Often, but certainly not always...