They are also far more powerful than werewolves and the most ancient of vampires. Funny thing is, is that the original vampires were necromancers who changed their souls and messed with their essence to become vampires, which is somewhat like how you become a lich, but it's much more complicated.
Where are you getting this information? Some other fantasy world? The original vampires were the creation of Lamae Beolfag, a Nede woman who was violated by Molag Bal, died, then rose from the dead. I need a source on this idea that the "original vampries" were necromancers.
Liches don't blend in well with society. Maybe a master of Illusion could trick the stupid, but any competent being would see through it and so you'd hardly be safe anywhere. Even Jagar Tharn's Illusions didn't fool everyone, and he was the greatest Illusionist to date.
Plus, as I said before, there is no cure for Lichdom. Your character would have to die to become a Lich, and there's no cure for death. If a player became a Lich and decided he/she did not like it, then that's just too bad, as they're now stuck with a Lich forever.