Some additional comments explaining all the option in the config file would be good, or a wiki maybe?

In particular, I'm not really clear on what the randomChance and randomFactor option do? Do they just allow for some random variation in mod levels?

If you want you can edit the readme section and add a wiki part to it :)
the randomChance applies when allowRandomValues is set to true.
it basically sets the chance for having a random values on the spawning mob

Added some info to the readme with 7acb644