I agree, you'll need your ghoul unit to be at least 30 strong, I'd say drop heroes for that.
I like the idea of a black coach in that size game but as you said, you might not need it. I say you'll need some dire wolves or fell bats, only 1-2 units, no need to overdo it, maybe drop the skellys for that and get dire wolves and a little tar pit of zombies, say 30 strong again, there easy to learn tactics with for a beginner.
Maybe even grab a single spirit host, a bit harder to learn how to use well but they are a unique aspect of our army and are worth knowing how to use