Unless the Nagash book is the way things are going to be once 9th Ed rolls around, I wouldn't put to much stock into the funky rules in there. From what I can tell it's just another supplement like Storm of Magic was. I would concentrate on the rules in the BRB and whichever army book you choose to use.I'll start by buying the nagash book and getting ideas from that, afterwards I'll probley get the tomb kings and see what there like.
I play VC as one of my armies and, while not hard to play, the strategies vary quite a bit due to the different ways in which they calculate combat, how much they rely on magic to keep the army moving/replenished (more so the latter), how horrid their Core choices are in combat (worse than Gobbos!), etc. So, like TK, easy to play if you know the basic rules, a little different to master. However, if you're not starting a new army after having played a "normal" race, it may not make to much of a difference as you'll have nothing to compare it to.