Should the starting hero for Necropolis be chosen randomly?

Try playing as Necropolis in the Test Environment; everything is possible there.
And free skeletons don't accumulate. It's a good castle for gameplay. You build and buy fairly, just like with all the other castles.
I recommend it to get a complete understanding of the Necropolis faction. Playing without upgraded vampires is no longer playing as Necropolis; it's just a parody.