Overpowered compared to what? Neferata's entire Blood Court formation? A vampire on Zombie Dragon? 200 Zombies? A single Skeleton? Nagash?
Balance in Age of Sigmar is arbitrary to begin with.
Once your group determines what they think it's worth, then it's balanced when played against that much opposing stuff. Just like everything else in the game. If you use one of the common points systems, I'm sure they'll put out points values for this FW packet soon enough, too.
Lots of things break wound point limits. Anything that halves wounds (ushabti, sphinxes), anything that emphasizes offence (offensive elite infantry). Again, Nagash. This guy's strong, but that system's bust regardless.
Nice to see I'm not the only one who thinks the model looks silly, I've actually heard from a lot of people that they love it. I like the concept but I think it lacks detail and reminds me of the 'Scream' movie mascot.
Probably drop the orb thing but I think its the right size and theme for a nighthaunt monster.
Regarding Wound Count - just don't. It is the worst way to play, even worse than playing the rules as written and is like a poison to the hobby. Just pick any other way to play and you will have a much better time.