Re: Fitness
Any preparative training will increase your enjoyment and decrease strain on the trail. That is not to say that you necessarily need any - depends on your starting condition I guess. Any how much you intend to push yourself (how many hours a day will you walk? carry your own gear?). As Mr Average, I find that with no prep, a relaxed week on the trail with a pack will get me walk-fit.
There is little worry from AMS below say 3000m (possibly as low as 2500m). As sharp rise above 3000m can cause a problem. General principal sleep low/walk high.
rich
No one goes so far or so fast as the man who does not know where he is going. H.W.Tilman